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

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mikomikotaishi wrote:

> I still don't see the need to interleave parts of the string with expressions.

Why is this a problem? If this introduced cognitive complexity or was otherwise unclear, I would see why, but this example is so trivial that I highly doubt it could.

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