install python for blst nightly checks before building instead of after

[altendky]

https://github.com/Chia-Network/bls-signatures/actions/runs/11468270388

[coveralls-official[bot]]

Pull Request Test Coverage Report for Build 11468376882

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.649%

---

Totals
Change from base Build 11407218133:	0.0%
Covered Lines:	1645
Relevant Lines:	1738

---

💛 - Coveralls

[hoffmang9]

lgtm but seems I can't approve anymore