[clang] [clang-format][NFC] Replace a function with StringRef::contains (PR #146245)

[Björn Schäpers via cfe-commits]

https://github.com/HazardyKnusperkeks commented:

While it is less code, I find a bit harder to understand and the code gen is far worse: https://gcc.godbolt.org/z/KzG4YnTh3

https://github.com/llvm/llvm-project/pull/146245