[clang] [Clang][Sema] fix a bug on constraint check with template friend function (PR #90646)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

I agree with @sdkrystian, even though the test crashes for maybe yet another reason, it demonstrates you can friend a function from a different template context, so comparing the depths from different branches is not helpful.

https://github.com/llvm/llvm-project/pull/90646