[clang] [clang]Fix the StringRef assertion failure for non-narrow strings. (PR #212108)

[Hardik Kumar via cfe-commits]

hardikxk wrote:

I just figured out the tests thanks to the [clang docs](https://clang.llvm.org/docs/InternalsManual.html#verifying-diagnostics)

https://github.com/llvm/llvm-project/pull/212108