CHANGELOG update after v1.3.6 release

[carmocca]

What does this PR do?

CHANGELOG update + Legacy checkpoint update

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• [n/a] Did you write any new necessary tests? (not for typos and docs)
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• Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

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[codecov]

Codecov Report

Merging #7988 (218c650) into master (7978a53) will decrease coverage by 5%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #7988    +/-   ##
=======================================
- Coverage      92%     87%    -5%     
=======================================
  Files         207     207            
  Lines       13484   13484            
=======================================
- Hits        12354   11713   -641     
- Misses       1130    1771   +641