fix auto scale batch size not working with precision=16

[awaelchli]

What does this PR do?

Fixes #3025
Fixes #2655 (we may need an extra test)

Made sure test is failing on master

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[codecov]

Codecov Report

Merging #3045 into master will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #3045    +/-   ##
=======================================
- Coverage      90%     86%    -4%     
=======================================
  Files          81      81            
  Lines        7673    7673            
=======================================
- Hits         6913    6605   -308     
- Misses        760    1068   +308     

[SkafteNicki]

LGTM

[mergify]

Great job! =)