Fix SWA with a list of learning rates

[carmocca]

What does this PR do?

No issue, found reading the code.

Does your PR introduce any breaking changes? If yes, please list them.

None

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[codecov]

Codecov Report

Merging #8747 (4539d6d) into master (24f0124) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #8747   +/-   ##
======================================
  Coverage      93%     93%           
======================================
  Files         169     169           
  Lines       14078   14076    -2     
======================================
- Hits        13052   13051    -1     
+ Misses       1026    1025    -1