[llvm] [mlir] [CI] Add check-mlir-python to MLIR pre-merge checks (PR #72847)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

>  I'm thinking of the case where MLIR bumps python/pybind11/numpy version and the image need to be updated in order for that change to land.


Better update the test script to run `pip install -r mlir/python/requirements.txt`?

https://github.com/llvm/llvm-project/pull/72847