[clang] [NFC][CLANG] Fix static analyzer bugs about unnecessary object copies with auto keyword (PR #85962)

[Tom Honermann via cfe-commits]

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

This looks fine to me. `LambdaCapture` consists of a pointer and two source locations so is relatively small and thus, this doesn't address a performance concern. Having the variable be `const` is good regardless to avoid unintended mutation.

https://github.com/llvm/llvm-project/pull/85962