[llvm] [GitHub][workflows] Use latest clang-format version 18.1.1 (PR #85502)

[Owen Pan via llvm-commits]

owenca wrote:

> Is it possible to include a short summary in the commit message next time?

Because I remembered that using the latest release of clang-format for the github workflow had already been decided, I didn't feel that any reason or justification was needed (other than 18.1.1 had been released for more than a week). Otherwise, I would have added an explanation in the commit message.

https://github.com/llvm/llvm-project/pull/85502