py-asyncpg: updated to 0.27.0

v0.27.0

Support Python 3.11 and PostgreSQL 15. This release also drops support
for Python 3.6.

Changes

Add arm64 mac and linux wheels
Add Python 3.11 to the test matrix
Exclude .venv from flake8
Upgrade to flake8 5.0.4 (from 3.9.2)
Show an example of a custom Record class
Use the exact type name in Record.repr
Drop Python 3.6 support
Test on Python 3.11 and PostgreSQL 15, fix workflow deprecations

(adam)