Removing support for Python 3.8

[timryanb]

• Python 3.8 will reach end of life in October. While there's still a couple months left until this happens some of our dependencies (numpy and pynastran) have already dropped support for it
• We are removing support for 3.8 early, as maintaining it is becoming more difficult due to the point above. Support in TACS has already been removed
• See TACS PR #289 for more info

[sean-engelstad]

Looks good, just concerned about the python 3.12 with conda.

[sean-engelstad]

Last time I tested python 3.12 with the conda build of funtofem it didn't work.

[timryanb]

I also ran into issues building against 3.12 when it first came out. It tends to take a while for all of our dependencies to upgrade their conda packages for new Python versions.

That said, a 3.12 build for funtofem will definitely fail at the moment since TACS doesn't have any Python 3.12 conda packages (and tacs is listed as a dependency for funtofem in the conda recipe). I tested out building a conda package for tacs on 3.12 this morning and seemed to have success. So 3.12 support should be available on the tacs side with the new tacs version bump this week.