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

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> @Endilll Hi, sorry for the two-day wait. We're using str.format() now

No worries, work when you can and want to. It's not my intention to burn out contributors with deadlines.

In the future please refrain from rebasing the branch, because it makes it harder for reviewers to see history of the changes. Merge commits are not a problem, because PRs are squashed upon merging.

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