Fix test compatibility with pytest-asyncio >= 1.0.0

[mgorny]

Replace the obsolete event_loop fixture with
asyncio.get_running_loop(), to fix testing with newer versions of pytest-asyncio. This change is backwards compatible.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a0bb32b) to head (2ef7cba).
⚠️ Report is 6 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff            @@
##            master       #53   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          113       113           
=========================================
  Hits           113       113           

Flag	Coverage Δ
unit	100.00% <ø> (ø)

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