[clang] [clang] fix lack comparison of declRefExpr in ASTStructuralEquivalence (PR #66041)

[via cfe-commits]

cor3ntin wrote:

You should edit `clang/docs/ReleaseNotes.rst`, indicating that https://github.com/llvm/llvm-project/issues/66047 was fixed, 
and edit the description of the PR with `Fixes #66047` so that it gets closed automatically.

Otherwise LGTM

https://github.com/llvm/llvm-project/pull/66041