[Clang] Assertion failure in `Sema::DeclareAggregateDeductionGuideFromInitList` when using CTAD with alias templates

***Generated by fuzzer.***
Clang trunk crashed and goes back to 19.1.
Compiler Explorer: https://godbolt.org/z/6oaj86rnq

## Program
```cpp
import M; template < typename > struct A{int u } template < class T > using B = A< T >;
b_type(B{})
```

## Stack Dump
```bash
:1:8: fatal error: module 'M' not found
1 | import M; template < typename > struct A{int u } template < class T > using B = A< T >;
| ~~~~~~~^
clang++: /root/llvm-project/llvm/include/llvm/Support/Casting.h:572: decltype(auto) llvm::cast(From*) [with To = clang::CXXRecordDecl; From = clang::NamedDecl]: Assertion `isa(Val) && "cast() argument of incompatible type!"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++23
1. :2:11: current parser token ')'
#0 0x000000000430a6b8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x430a6b8)
#1 0x0000000004307b14 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4307b14)
#2 0x0000000004249de8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#3 0x00007f6ee2e42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
#4 0x00007f6ee2e969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
#5 0x00007f6ee2e42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
#6 0x00007f6ee2e287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
#7 0x00007f6ee2e2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
#8 0x00007f6ee2e39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
#9 0x00000000075659ff clang::Sema::DeclareAggregateDeductionGuideFromInitList(clang::TemplateDecl*, llvm::MutableArrayRef, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x75659ff)
#10 0x0000000007133141 clang::Sema::DeduceTemplateSpecializationFromInitializer(clang::TypeSourceInfo*, clang::InitializedEntity const&, clang::InitializationKind const&, llvm::MutableArrayRef)::'lambda0'(bool)::operator()(bool) const::'lambda'(clang::InitListExpr*)::operator()(clang::InitListExpr*) const SemaInit.cpp:0:0
#11 0x0000000007133682 clang::Sema::DeduceTemplateSpecializationFromInitializer(clang::TypeSourceInfo*, clang::InitializedEntity const&, clang::InitializationKind const&, llvm::MutableArrayRef)::'lambda0'(bool)::operator()(bool) const SemaInit.cpp:0:0
#12 0x0000000007133d75 clang::Sema::DeduceTemplateSpecializationFromInitializer(clang::TypeSourceInfo*, clang::InitializedEntity const&, clang::InitializationKind const&, llvm::MutableArrayRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7133d75)
#13 0x000000000708d60d clang::Sema::BuildCXXTypeConstructExpr(clang::TypeSourceInfo*, clang::SourceLocation, llvm::MutableArrayRef, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x708d60d)
#14 0x000000000708db39 clang::Sema::ActOnCXXTypeConstructExpr(clang::OpaquePtr, clang::SourceLocation, llvm::MutableArrayRef, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x708db39)
#15 0x0000000006afb2e6 clang::Parser::ParseCXXTypeConstructExpression(clang::DeclSpec const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6afb2e6)
#16 0x0000000006adf670 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, bool&, clang::TypoCorrectionTypeBehavior, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6adf670)
#17 0x0000000006ae0217 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, clang::TypoCorrectionTypeBehavior, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ae0217)
#18 0x0000000006ae02a9 clang::Parser::ParseAssignmentExpression(clang::TypoCorrectionTypeBehavior) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ae02a9)
#19 0x0000000006ae060e clang::Parser::ParseExpressionList(llvm::SmallVectorImpl&, llvm::function_ref, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ae060e)
#20 0x0000000006a998da clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a998da)
#21 0x0000000006aa702a clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6aa702a)
#22 0x0000000006a6472b clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a6472b)
#23 0x0000000006a64f1f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a64f1f)
#24 0x0000000006a6cd4a clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a6cd4a)
#25 0x0000000006a6dce5 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a6dce5)
#26 0x0000000006a4ed6a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a4ed6a)
#27 0x0000000004c722a8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c722a8)
#28 0x0000000004f6bc55 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4f6bc55)
#29 0x0000000004eeb8de clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4eeb8de)
#30 0x000000000506698d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x506698d)
#31 0x0000000000ddcf9e cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xddcf9e)
#32 0x0000000000dd396a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#33 0x0000000000dd3aed int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#34 0x0000000004ce55a9 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#35 0x000000000424a284 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x424a284)
#36 0x0000000004ce5bbf clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#37 0x0000000004ca6592 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ca6592)
#38 0x0000000004ca753e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ca753e)
#39 0x0000000004cae985 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4cae985)
#40 0x0000000000dd9311 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdd9311)
#41 0x0000000000c969c4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc969c4)
#42 0x00007f6ee2e29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#43 0x00007f6ee2e29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#44 0x0000000000dd3405 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdd3405)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```

Reproduce the assertion with the C++ program and compiler invocation from the issue, using the linked Compiler Explorer example as a reference. Start in clang::Sema::DeclareAggregateDeductionGuideFromInitList, then trace the call through DeduceTemplateSpecializationFromInitializer. Done means the alias-template CTAD case no longer triggers the assertion and has regression coverage.

Written by the indexing model from the issue text.