[clang] [clang][Python] Use fstrings instead of string concatenations (PR #173861)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Also, I prefer to resolve conversations myself, so that I can check that my feedback was addressed correctly.
But I apologize in advance if a different reviewer will tell you something else, because each of us have different preferences when it comes to review workflow.

https://github.com/llvm/llvm-project/pull/173861