[clang-tools-extra] [clang-tidy] Fix result check after overwriteChangedFiles() (PR #86360)

[Mike Rice via cfe-commits]

mikerice1969 wrote:

> This could use a test.

I thought about it, but I have no idea how to write that test. Do you have an idea?

https://github.com/llvm/llvm-project/pull/86360