[clang-tools-extra] [clang-tidy][NFC] fix add_new_check python3.8 incompatibility (PR #107871)

[Congcong Cai via cfe-commits]

HerrCai0907 wrote:

actually both are fine. since 3.8 will stop maintain soon. It just a temp solution and may be alive only in half year.

https://github.com/llvm/llvm-project/pull/107871