docs(changelog): add 1.20.2 release notes

[mr-cal]

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• Have you successfully run tox?

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This release is intended for snapcraft 7.x. The integration tests will fail to launch almalinux 9, but that's OK because snapcraft doesn't use alma.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.01%. Comparing base (2854264) to head (7ab1dd6).

Additional details and impacted files

@@             Coverage Diff              @@
##           hotfix/1.20     #536   +/-   ##
============================================
  Coverage        99.01%   99.01%           
============================================
  Files               57       57           
  Lines             4561     4561           
============================================
  Hits              4516     4516           
  Misses              45       45           

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