test: increase MotoService start timeout

[Xeonacid]

Description of Change

It takes about 15s on a RISC-V Unmatched SBC to start. Change it to 20s.

Assumptions

Replace this text with any assumptions made (if any)

Checklist for All Submissions

• [ ] I have added change info to CHANGES.rst

  Does this change for a test need to update the file? If so, please tell me, thanks.

• [ ] 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[bot]]

Codecov Report

Merging #1053 (b00b0b2) into master (48a3f37) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1053   +/-   ##
=======================================
  Coverage   86.39%   86.39%           
=======================================
  Files          60       60           
  Lines        5807     5807           
=======================================
  Hits         5017     5017           
  Misses        790      790           

Flag	Coverage Δ
unittests	86.39% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
tests/moto_server.py	81.91% <100.00%> (ø)

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