bump: drop support for python 3.8

[Borda]

What does this PR do?

Python 3.8 is not live, let's bump...
https://endoflife.date/python

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--2827.org.readthedocs.build/en/2827/

[codecov]

Codecov Report

Attention: Patch coverage is 96.93431% with 21 lines in your changes missing coverage. Please review.

Project coverage is 69%. Comparing base (bf030e0) to head (00bb215).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #2827    +/-   ##
=======================================
  Coverage      69%     69%            
=======================================
  Files         344     344            
  Lines       18831   18970   +139     
=======================================
+ Hits        12978   13116   +138     
- Misses       5853    5854     +1     

[Borda]

asking the annotation fixing in astral-sh/ruff#14112

ann = list[torch.Tensor], loc = 

    def ann_to_type(ann, loc):
        the_type = try_ann_to_type(ann, loc)
        if the_type is not None:
            return the_type
>       raise ValueError(f"Unknown type annotation: '{ann}' at {loc.highlight()}")
E       ValueError: Unknown type annotation: 'list[torch.Tensor]' at

for python 3.10

[lantiga]

LGTM

wdyt @SkafteNicki ?