Adapt to new universal polynomial base_ring

[SoongNoonien]

This makes GenericCharacterTables compatible with Nemocas/AbstractAlgebra.jl#2182.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.27%. Comparing base (000f767) to head (987f5ed).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #306   +/-   ##
=======================================
  Coverage   95.27%   95.27%           
=======================================
  Files          14       14           
  Lines         973      973           
=======================================
  Hits          927      927           
  Misses         46       46           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.