Replace ubuntu-20.04 with 22.04 in CI

[mrbean-bremen]

• ubuntu-20.04 is no longer supported, ubuntu-latest is now 24.04
• fix workflow syntax
• fix ruff syntax

I had noticed that most of the tests fail because they can't find a runner (my PR was merged, thanks for that!).

[mrbean-bremen]

Actually as was wrong - this did not run because of the syntax. Though ubuntu-20.04 is indeed deprecated and will soon be removed, this was not the problem.
And now the tests are all failing...

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #177   +/-   ##
=======================================
  Coverage        ?   93.27%           
=======================================
  Files           ?        8           
  Lines           ?      223           
  Branches        ?       50           
=======================================
  Hits            ?      208           
  Misses          ?        7           
  Partials        ?        8           

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[mrbean-bremen]

Ok, this is ready for review now.
(in case you saw that: I had accidentally checked in a change in pyproject.toml, appearantly made automatically by ux - reverted now)

[kislyuk]

LGTM, thanks!