[llvm] [Github] Allow CI to run different Python version tests at once (PR #102455)

[Jannick Kremer via llvm-commits]

DeinAlptraum wrote:

@boomanaiden154 yup, you can see on the CI for this branch that it ran the tests for both versions, and I've tested on my fork that it still correctly cancels simultaneous runs for the same version.

Thanks for reviewing!

On another note, now that I think about it, is there any need to actually run the build twice? Shouldn't it be sufficient to build libclang once, and then just run the Python tests with separate Python versions? 

https://github.com/llvm/llvm-project/pull/102455