Avoid pulling outdated container images in mototest make target

[jakob-keller]

Description of Change

Avoid pulling outdated container images in mototest make target

Assumptions

We aim to use default images "for recent versions" as documented by moto.

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): closes Modernize Lambda in unit tests #1267
  • 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 87.56%. Comparing base (fb860e8) to head (5ff7a4e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1268      +/-   ##
==========================================
+ Coverage   87.48%   87.56%   +0.08%     
==========================================
  Files          67       67              
  Lines        5905     5905              
==========================================
+ Hits         5166     5171       +5     
+ Misses        739      734       -5     

Flag	Coverage Δ
unittests	87.56% <ø> (+0.08%)	⬆️

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