[clang-tools-extra] [clang-doc] [test] Generalize error message patterns (PR #142373)

[Samarth Narang via cfe-commits]

snarang181 wrote:

@ilovepi, for this check, should we just be looking for "clang doc error: " and remove the directory substring matching entirely?  

https://github.com/llvm/llvm-project/pull/142373