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

[Donát Nagy via cfe-commits]

NagyDonat wrote:

> My intention was to ease the review as much as possible by cutting them into atomic parts.

This is a good idea in general, but I feel that these two changes are so trivial, that they'd be very easy to review even together. Feel free to merge them both in whatever combination you would like. 

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