[clang-tools-extra] [clang-doc] lower filename length limit by 5 (PR #155511)

[Paul Kirth via cfe-commits]

ilovepi wrote:

> LGTM, but I thought we had a unit test for this? Am I misremembering?

Looking at the source: I am wrong and we never had one.

https://github.com/llvm/llvm-project/pull/155511