don't require Python 3.10

[mwermelinger]

A tutor found that allowed crashes on the briefing notebook in a new M269 24J installation in Raspberry Pi. More generally, it crashes with option -m when pytype is installed but Python 3.10 isn't. To recreate on macOS,

1. do PATH=/usr/bin:/bin so that the Python binary links in /usr/local/bin aren't found
2. do m269-24j to activate the M269 environment and change to the M269 folder
3. do allowed -m book-r1/python/m269_test.py

To fix this, need probably to revert to old check of whether allowed is being run under Python 3.10 or 3.11. The comment in PR #57 seems to indicate I hardwired 3.10 to make it work with old pytype versions.

• change allowed.py
• re-run all tests
• make new 1.5.1 release