[llvm] Fix update-test-checks.py on Python 3.6 (PR #93116)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

Python 3.6 reached end of life in December 2021, so well over 2 years ago. Do we really need to support it? Is updating to a newer python not an option in this case?

https://github.com/llvm/llvm-project/pull/93116