update tests to not rely on patched dataloaders

[awaelchli]

What does this PR do?

Splits out changes from #9764

The changed tests here rely on accessing the patched model.x_dataloader().
Making this a separate PR ensures the integrity of the tests and that there is no unintended coupling with changes in #9764.

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Did you have fun?

I made sure I had fun coding 🙃

[SeanNaren]

LGTM!

[tchaton]

LGTM !

[codecov]

Codecov Report

Merging #9905 (f187078) into master (f16bfe9) will decrease coverage by 1%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #9905    +/-   ##
=======================================
- Coverage      93%     92%    -1%     
=======================================
  Files         178     178            
  Lines       15647   15796   +149     
=======================================
+ Hits        14502   14559    +57     
- Misses       1145    1237    +92