[clang][Sema] Skip the RequiresExprBodyDecls for lambda dependencies (#83997)

The dependency of a lambda inside of a `RequiresExprBodyDecl` was
previously affected by its parent, e.g.,
`ClassTemplateSpecializationDecl`. This made the lambda always dependent
regardless of the template arguments we had, which caused some crashes
on the constraint evaluation later.

This fixes https://github.com/llvm/llvm-project/issues/56556, fixes
https://github.com/llvm/llvm-project/issues/82849 and a case
demonstrated by
https://github.com/llvm/llvm-project/issues/49570#issuecomment-1664966972.