Update python to >= 3.9

[MikeLippincott]

          I recommend decoupling CellProfiler from the preprocessing software in the future due to the Python 3.8 end-of-life issue that is isolated to CellProfiler. There seems to be a solution by installing CP v4.2.7, which is Python 3.9 compatible. This might be out of scope for this PR.

Originally posted by @jenna-tomkinson in #10 (comment)