Update CI workflows including cutting Python v3.10 support

[sadielbartholomew]

Close #964 (next release will be after the October v3.10 EOL) and close #969 whilst updating the CI/Actions workflows (which could do with many bumps on the external Actions versions) and also testing the new build command for #966.

[sadielbartholomew]

Closing and re-opening to refresh the CI jobs matrix...

[sadielbartholomew]

Another open-close for CI job refresh - seems to pick up the edited workflows whereas clicking the 're-run jobs' buttons doesn't sometimes...

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #967   +/-   ##
=======================================
  Coverage        ?   82.90%           
=======================================
  Files           ?      105           
  Lines           ?    17123           
  Branches        ?        0           
=======================================
  Hits            ?    14194           
  Misses          ?     2929           
  Partials        ?        0           

Flag	Coverage Δ
unittests	82.90% <ø> (?)

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[sadielbartholomew]

OK the Ubuntu CI jobs are now passing, finally. I commented out the latest Mac OS as an <job>.strategy.matrix.os option since I suspect there is a separate issue there causing all jobs to fail early, but I am now adding that back in to see. There is a further issue with the test-source-dist.yml workflow but I think that is close to passing now. Let's see...

[sadielbartholomew]

test-source-dist.yml workflow now also passing but there is an early failure with the Mac OS case. Trying again...

[sadielbartholomew]

Now all running but the Mac OS and Ubuntu runs seem to have picked up on some genuine issues (possible bugs), so noting those and investigating separately. Now adding in missing optional dependencies to the workflows so we don't have any avoidable test skipping on the jobs.

[sadielbartholomew]

One last time to run the jobs after pushing a fix for one trivial issue raised by one particular job, and then I am satisfied to merge because the remaining failures are genuine issues raised (see #968, NCAS-CMS/cfdm#429).