move batch to device before sending it to hooks

[awaelchli]

What does this PR do?

Fixes #7377
Fixes #6990

In the loops we have the following structure:

on_train_batch_start(batch)  # master: batch on CPU, this PR: batch is on GPU
accelerator.training_step(batch) # master: batch gets moved to GPU here, this PR: batch is already on GPU here
on_train_batch_end(batch)  # master: batch on CPU, this PR: batch is on GPU

Test fails on master.

Open to suggestions for a more elegant way to test.

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[codecov]

Codecov Report

Merging #7378 (542efbd) into master (8193bae) will decrease coverage by 5%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #7378    +/-   ##
=======================================
- Coverage      93%     88%    -5%     
=======================================
  Files         212     212            
  Lines       13720   13716     -4     
=======================================
- Hits        12751   12070   -681     
- Misses        969    1646   +677     

[awaelchli]

Re-requesting review from all. Since the creation of this PR we moved to the new loop API.

[tchaton]

LGTM !

[kaushikb11]

LGTM!