[llvm] [MLGO] Remove Python <3.8 from unsupported config (PR #106132)

[via llvm-commits]

dyung wrote:

@boomanaiden154 your change seems to be causing a test failure of `llvm/test/CodeGen/MLRegAlloc/interactive-mode.ll' on a bot.

https://lab.llvm.org/buildbot/#/builders/174/builds/3975

Can you take a look and revert if you need time to investigate?

https://github.com/llvm/llvm-project/pull/106132