fix: remove catch protections for unscaled AMP types for gradient scaler

[vsandwar-sumer]

What does this PR do?

This PR resolves a bug introduced in #15555 that caused errors to occur when a user trains a model with bf16-mixed which doesn't have a scaler, gradient clipping and fused adamW optimizer. The protection was there as AMPs with scaler would clash with the fused optimizer as the scaling was contained in the process. However, it only checked if the optimizer required internal scaling and not whether the AMP datatype did. Adding an additional condition there should resolve this issue.

Fixes #21435

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📚 Documentation preview 📚: https://pytorch-lightning--21436.org.readthedocs.build/en/21436/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79%. Comparing base (2e25642) to head (7a52a99).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

❗ There is a different number of reports uploaded between BASE (2e25642) and HEAD (7a52a99). Click for more details.

HEAD has 385 uploads less than BASE

Flag	BASE (2e25642)	HEAD (7a52a99)
cpu	119	30
lightning_fabric	30	0
pytest	60	0
python3.12	36	9
lightning	59	15
python3.11	23	6
python3.12.7	36	9
python3.10	12	3
python	12	3
pytorch2.9	6	3
pytorch_lightning	30	15
pytest-full	59	30
pytorch2.1	12	6
pytorch2.7	6	3
pytorch2.8	6	3
pytorch2.2.2	6	3
pytorch2.4.1	6	3
pytorch2.5.1	6	3
pytorch2.3	5	3
pytorch2.6	6	3

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #21436     +/-   ##
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- Coverage      87%      79%     -8%     
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  Files         270      267      -3     
  Lines       24059    24004     -55     
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- Hits        20859    18952   -1907     
- Misses       3200     5052   +1852