CI: Update GHA config

[hugovk]

• There's no need for the "drop the dot" workaround, it will use the interpreter tox is installed to
• Also test on Python 3.8
• pre-commit autoupdate

[codecov[bot]]

Codecov Report

Merging #451 into master will not change coverage. The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #451   +/-   ##
======================================
  Coverage    90.4%   90.4%           
======================================
  Files          28      28           
  Lines        2585    2585           
======================================
  Hits         2337    2337           
  Misses        248     248

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 8f39ac5...1e0b3fd. Read the comment docs.