science/py-scipy: Fix required python version
scipy dropped support for 3.6 as of 1.6.0:
https://github.com/scipy/scipy/commit/0a4f408d9bd560f9a379d2e33b136b93f3583042
PR: 256083
MFH: 2021Q2
(cherry picked from commit 7a75d1c97ab2c2b41d32490b31ffb07c55800ee7)