[mlir] Limit Python dependency to Development.Module when possible.

After CMake 3.18, we are able to limit the scope of the
find_package(Python3 ...) search to just Development.Module. Searching
for Development will fail in manylinux builds, and isn't necessary
since we are not embedding the Python interpreter. For more information, see:
https://pybind11.readthedocs.io/en/stable/compiling.html#findpython-mode

Reviewed By: stellaraccident

Differential Revision: https://reviews.llvm.org/D111383