[Bug]: NullPointerException with `__debug__` type alias

Describe the bug

GraalPy crashes when running this fuzzed code:

type __debug__ = int

Operating system

Linux

CPU architecture

x86_64

GraalPy version

GraalPy 3.13.14 (Oracle GraalVM Native 25.3.4.1)

JDK version

No response

Context configuration

No response

Steps to reproduce

Snippet listed above

Expected behavior

No crash

Stack trace

java.lang.NullPointerException: Stack trace is imprecise, the top frames are missing and/or have wrong line numbers. To get precise stack traces, build the image with option -H:-ReduceImplicitExceptionStackTraceInformation
	at org.graalvm.py/com.oracle.graal.python.compiler.ParserCallbacksImpl.raiseSyntaxError(ParserCallbacksImpl.java:126)
	at org.graalvm.py/com.oracle.graal.python.compiler.ParserCallbacksImpl.raiseSyntaxError(ParserCallbacksImpl.java:122)
	at org.graalvm.py/com.oracle.graal.python.compiler.ParserCallbacksImpl.onError(ParserCallbacksImpl.java:118)
	at org.graalvm.py/com.oracle.graal.python.compiler.SSTUtils.checkForbiddenName(SSTUtils.java:90)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.checkForbiddenName(RootNodeCompiler.java:667)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.checkForbiddenName(RootNodeCompiler.java:658)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.emitNameOperation(RootNodeCompiler.java:1817)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.beginStoreLocal(RootNodeCompiler.java:1859)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler$StatementCompiler.visit(RootNodeCompiler.java:6976)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler$StatementCompiler.visit(RootNodeCompiler.java:2001)
	at org.graalvm.py/com.oracle.graal.python.pegparser.sst.StmtTy$TypeAlias.accept(StmtTy.java:216)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.visitModuleBody(RootNodeCompiler.java:1090)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.lambda$visit$0(RootNodeCompiler.java:1007)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen$Bytecode.create(PBytecodeDSLRootNodeGen.java:4988)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen.create(PBytecodeDSLRootNodeGen.java:3790)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.compileRootNode(RootNodeCompiler.java:530)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.visit(RootNodeCompiler.java:1005)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.visit(RootNodeCompiler.java:186)
	at org.graalvm.py/com.oracle.graal.python.pegparser.sst.ModTy$Module.accept(ModTy.java:68)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.RootNodeCompiler.compile(RootNodeCompiler.java:755)
	at org.graalvm.py/com.oracle.graal.python.compiler.bytecode_dsl.BytecodeDSLCompiler.compile(BytecodeDSLCompiler.java:86)
	at org.graalvm.py/com.oracle.graal.python.PythonLanguage.compileForBytecodeDSLInterpreter(PythonLanguage.java:661)
	at org.graalvm.py/com.oracle.graal.python.PythonLanguage.compileModule(PythonLanguage.java:633)
	at org.graalvm.py/com.oracle.graal.python.PythonLanguage.parse(PythonLanguage.java:601)
	at org.graalvm.py/com.oracle.graal.python.PythonLanguage.parse(PythonLanguage.java:588)
	at org.graalvm.py/com.oracle.graal.python.PythonLanguage.parse(PythonLanguage.java:574)
[...snip...]

Additional context

No response

Start with the failing snippet type __debug__ = int and trace the reported path through SSTUtils.checkForbiddenName and RootNodeCompiler. Reproduce it on GraalPy 3.13.14, then add a regression test using the snippet. Done means the input no longer crashes with a NullPointerException and produces the expected language-level result.