[clang] [clang] Improve bit-field in ref NTTP diagnostic (PR #71077)

[Andrey Ali Khan Bolshakov via cfe-commits]

bolshakov-a wrote:

> Can you add a release note?

Do you think this small diagnostic wording change is worth noting in relnotes?

> Do we need more tests in other contexts where a converted constant expression is used?

Seems like constant expressions converted to references may currently only appear in non-type template arguments. Added a case into `SemaTemplate/temp_arg_nontype_cxx20.cpp`.

https://github.com/llvm/llvm-project/pull/71077