Nightly CI for software using FLINT

[albinahlback]

I'm thinking of:

• msolve
• Sage (See CI: Add portability and integration tests with passagemath #1760)
• Singular
• Macaulay2
• Change Nemo CI to nightly.

[fredrik-johansson]

• python-flint

[albinahlback]

I think this is good to pursue at the workshop.

[mkoeppe]

You can get msolve, python-flint, singular for free with the Sage CI from #1760 (and sagemath/sage#37224)

[edgarcosta]

I am happy to look into this at the workshop