Bump pytest-asyncio dev dependency

[jakob-keller]

Description of Change

Bump pytest-asyncio dev dependency

Assumptions

None

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 86.18%. Comparing base (6827354) to head (828bec9).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1141   +/-   ##
=======================================
  Coverage   86.18%   86.18%           
=======================================
  Files          62       62           
  Lines        5944     5944           
=======================================
  Hits         5123     5123           
  Misses        821      821           

Flag	Coverage Δ
unittests	86.18% <ø> (ø)

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