tests: Support dashes in test suite names

[sentrivana]

• actually support dashes in integration names in tox.ini/toxgen
• make split_tox_gh_actions.py actually fail if it fails to parse tox.ini

Context: split_tox_gh_actions.py was actually failing because it assumed there can't be dashes in test suite names, but since it was just printing the error instead of actually exiting with an error code, we didn't notice this in CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.87%. Comparing base (f702ec9) to head (ef74285).
⚠️ Report is 4 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4740      +/-   ##
==========================================
- Coverage   84.89%   84.87%   -0.03%     
==========================================
  Files         156      156              
  Lines       16115    16115              
  Branches     2741     2741              
==========================================
- Hits        13681    13677       -4     
- Misses       1645     1649       +4     
  Partials      789      789              

see 1 file with indirect coverage changes