[clang] [clang][analyzer][NFC] Improve docs of alpha.unix.BlockInCriticalSection (PR #93812)

[Donát Nagy via cfe-commits]

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

What's the relationship between this PR and https://github.com/llvm/llvm-project/pull/93799 ?

Otherwise, the change LGTM, but you might want to either unify these two NFC changes into a single commit or ensure that they're independent.

https://github.com/llvm/llvm-project/pull/93812