[clang-tools-extra] [include-cleaner] don't consider the associated header unused (PR #67228)

[Sam McCall via cfe-commits]

sam-mccall wrote:

Apologies & thanks all for the pings.
I unfortunately won't be active on llvm-project for a while (other work commitments), but I can get this landed.

https://github.com/llvm/llvm-project/pull/67228