CI fixes for Python 3.8 and Breezy
- testing/_utils/site.py: Add BRZ_EMAIL to support Breezy 3.0
- tox.ini: Replace py38 with py38-nocover in default envlist
- .gitlab-ci.yml: Replace py38 with py38-nocover in TOXENV
These changes should fix CI on Fedora 32 and other distros that use Python 3.8 and/or Breezy (Bazaar fork).