leverage pytest-asyncio test discovery mode auto

[jakob-keller]

Description of Change

Removes @pytest.mark.asynciodecorators from test functions, in line with pytest-asyncio recommendation.

Cherry picked from @thehesiod: f7a2f75

Assumptions

Replace this text with any assumptions made (if any)

Checklist for All Submissions

• I have added change info to CHANGES.rst
• If this is resolving an issue (needed so future developers can determine if change is still necessary and under what conditions) (can be provided via link to issue with these details):
  • Detailed description of issue
  • Alternative methods considered (if any)
  • How issue is being resolved
  • How issue can be reproduced
• If this is providing a new feature (can be provided via link to issue with these details):
  • Detailed description of new feature
  • Why needed
  • Alternatives methods considered (if any)

Checklist when updating botocore and/or aiohttp versions

• I have read and followed CONTRIBUTING.rst
• I have updated test_patches.py where/if appropriate (also check if no changes necessary)
• I have ensured that the awscli/boto3 versions match the updated botocore version

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.05%. Comparing base (e7d6ddf) to head (872ccc3).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1233      +/-   ##
==========================================
- Coverage   86.16%   86.05%   -0.12%     
==========================================
  Files          64       64              
  Lines        5986     5801     -185     
==========================================
- Hits         5158     4992     -166     
+ Misses        828      809      -19     

Flag	Coverage Δ
unittests	86.05% <ø> (-0.12%)	⬇️

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[jakob-keller]

Will follow up with more comprehensive PR