Avoid deprecated use of aiohttp in tests

[jakob-keller]

Description of Change

Replace deprecated aiohttp session.get() argument verify_ssl by ssl in tests. This should have been part of #1081.

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 ✅

Please upload report for BASE (master@44f279e). Learn more about missing BASE report.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1139   +/-   ##
=========================================
  Coverage          ?   86.16%           
=========================================
  Files             ?       62           
  Lines             ?     5933           
  Branches          ?        0           
=========================================
  Hits              ?     5112           
  Misses            ?      821           
  Partials          ?        0           

Flag	Coverage Δ
unittests	86.16% <ø> (?)

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