Regression when evaluating constant expression in dependent types

In c++20, the following program used to be compiled successfully in gcc and msvc but rejected in clang. But from C++23, clang also started accepted the program. Seems like a regression: [Demo](https://godbolt.org/z/vW7f3PEos)
```cpp
template
struct s{
constexpr static int n = N;
};

template
void test(T& t){
static_assert(t.n == 1);
}

int main(){
s<1> str;
test(str);
}
```
C++20's clang rejected this but C++23's clang accepts this.

Start with the linked Godbolt reproduction and compare Clang's C++20 and C++23 behavior for the dependent-type constant expression. Trace the relevant Clang constant-expression and dependent-type handling to identify the regression or standards change; done means the differing behavior is explained and a focused compiler regression test can be identified.

Written by the indexing model from the issue text.