[clang-tools-extra] Fix the modification detection logic in `ClangdLSPServer::applyConfiguration`. (PR #115438)

[Dmitry Polukhin via cfe-commits]

https://github.com/dmpolukhin approved this pull request.

I think it is unexpected side effect of https://reviews.llvm.org/D143436. The diff was written together https://reviews.llvm.org/D148663 that was rejected so this edge was accidentally broken.

https://github.com/llvm/llvm-project/pull/115438