Run kernel tests for all c++ kernels

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

This PR is part of a series of PRs to improve the testing of xeus-cpp kernels. The purpose of this first PR is to run the python kernel tests for all c++ kernels and not just a single kernel (currently xcpp20).

Fixes # (issue)

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Added/removed dependencies
• Required documentation updates

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.78%. Comparing base (27a9f21) to head (0a76d4b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #384   +/-   ##
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  Coverage   81.78%   81.78%           
=======================================
  Files          20       20           
  Lines         950      950           
  Branches       87       87           
=======================================
  Hits          777      777           
  Misses        173      173           

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[mcbarton]

This PR can almost certainly be done in fewer lines. Python is not my strong suit, and I've just done it in a way which was clear to me.

[mcbarton]

@JohanMabille pinging for review

The purpose of this PR is to make it so that all the c++ kernels are tested. Currently only 1 is tested. In future PRs I plan to expand this to test the new c kernels too. With xeus-cpp about to get debug kernels too, its useful that it has a mechanism to run test sets for multiple kernels.

[JohanMabille]

Awesome! Testing all the available kernels is something I should have done earlier, thanks for fixing it!