error: template template argument ... is more constrained than template template parameter ... when it's actually not

Given the following program:
```cpp
#include

template
concept some_concept = !std::is_same_v;

template
struct A1 {};

template
struct A2 {};

template typename T>
struct X {
template typename T_>
using change_t = X;
};

int main() {
auto x1 = X{};
auto x2 = typename decltype(x1)::template change_t{};
}
```
it gives the following error:
```
:19:17: error: template template argument 'A1' is more constrained than template template parameter 'T'
19 | auto x1 = X{};
| ^~
:12:44: note: 'T' declared here
12 | template typename T>
| ^
:7:8: note: 'A1' declared here
7 | struct A1 {};
| ^
```
It fails when trying to instantiate the template `X`. If we strip away some seemingly unrelated code however, it compiles just fine:
```cpp
#include

template
concept some_concept = !std::is_same_v;

template
struct A1 {};

template typename T>
struct X {

};

int main() {
auto x1 = X{};
}
```
Tested on clang trunk

Start by reproducing both the full and reduced programs on clang trunk, then compare the template-template argument constraint diagnostics during X instantiation. Trace the interaction introduced by change_t and verify that the full program accepts A1 while retaining the intended constraint checks for template arguments.

Written by the indexing model from the issue text.