Remove CI checks against GAP stable-4.9 (since this package requires GAP 4.10)

[wilfwilson]

There is also a problem in the CI when testing in the GAP stable-4.10 branch; the problem occurs when trying to compile the orb package. Perhaps this is because orb now requires GAP >=4.12?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.09%. Comparing base (6b260d6) to head (f6f9961).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #47   +/-   ##
=======================================
  Coverage   62.09%   62.09%           
=======================================
  Files           3        3           
  Lines         153      153           
=======================================
  Hits           95       95           
  Misses         58       58           

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[wilfwilson]

I'll merge since this is obviously a no-brainer.