Fix LearningRateMonitor logging with multiple param groups optimizer with no scheduler

[rohitgr7]

What does this PR do?

Fixes #10024

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[codecov]

Codecov Report

Merging #10044 (48d9678) into master (6701526) will decrease coverage by 0%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #10044    +/-   ##
========================================
- Coverage      93%      92%    -0%     
========================================
  Files         180      180            
  Lines       15895    16381   +486     
========================================
+ Hits        14726    15125   +399     
- Misses       1169     1256    +87     

[tchaton]

Neat !