sstsimulator
Increase minimum required Python version from 3.6 to 3.9
As part of the 15.0.0 internal release plan, we decided to perform a minimum required Python version bump. However, in the public announcement at http://sst-simulator.org/sstannouncements/2025/05/09/SST-v15.0.0-Released/, this was not included. Between that and not making the code modifications in the build system, it was mostly forgotten about.
Making this change doesn't require elements changes, since it picks up whatever Python is in the config file during compile time (for example, https://github.com/sstsimulator/sst-elements/blob/2120920858b871f1d14c719b393c2675149ff27a/config/sst_check_numpy.m4#L10).
This change consists of two required parts:
- Update the minimum required version in the build system
- Ensure the CI jobs are updated
I've marked this as major since it is technically breaking and was never announced.
