Fix logic in how metric states referencing is handled in MetricCollection

[SkafteNicki]

What does this PR do?

Fixes #2896

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📚 Documentation preview 📚: https://torchmetrics--2990.org.readthedocs.build/en/2990/

[Borda]

@SkafteNicki please check:

FAILED unittests/bases/test_collections.py::TestComputeGroups::test_check_compute_groups_items_and_values[keys-metrics1-expected1-preds1-target1] - AssertionError: assert False
 +  where False = _allclose_recursive(tensor([0, 0, 0]), tensor([4, 2, 2]))
 +    where tensor([0, 0, 0]) = getattr(MulticlassAccuracy(), 'tp')
 +    and   tensor([4, 2, 2]) = getattr(MulticlassAccuracy(), 'tp')
FAILED unittests/bases/test_collections.py::TestComputeGroups::test_check_compute_groups_items_and_values[keys-metrics2-expected2-preds2-target2] - AssertionError: assert False
 +  where False = _allclose_recursive(tensor([0, 0, 0]), tensor([4, 2, 2]))
 +    where tensor([0, 0, 0]) = getattr(MulticlassRecall(), 'tp')
 +    and   tensor([4, 2, 2]) = getattr(MulticlassRecall(), 'tp')
FAILED unittests/bases/test_collections.py::TestComputeGroups::test_check_compute_groups_items_and_values[keys-metrics4-expected4-preds4-target4] - AssertionError: assert False
 +  where False = _allclose_recursive(tensor([[0, 0, 0],\n        [0, 0, 0],\n        [0, 0, 0]]), tensor([[4, 2, 6],\n        [4, 2, 8],\n        [4, 8, 2]]))
 +    where tensor([[0, 0, 0],\n        [0, 0, 0],\n        [0, 0, 0]]) = getattr(MulticlassCohenKappa(), 'confmat')
 +    and   tensor([[4, 2, 6],\n        [4, 2, 8],\n        [4, 8, 2]]) = getattr(MulticlassCohenKappa(), 'confmat')
FAILED unittests/bases/test_collections.py::TestComputeGroups::test_check_compute_groups_items_and_values[keys-metrics5-expected5-preds5-target5] - AssertionError: assert False
 +  where False = _allclose_recursive(tensor([0, 0, 0]), tensor([4, 2, 2]))
 +    where tensor([0, 0, 0]) = getattr(MulticlassAccuracy(), 'tp')
 +    and   tensor([4, 2, 2]) = getattr(MulticlassAccuracy(), 'tp')

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 70%. Comparing base (0423a2c) to head (0e2e69d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #2990    +/-   ##
=======================================
+ Coverage      69%     70%    +1%     
=======================================
  Files         352     352            
  Lines       19663   19663            
=======================================
+ Hits        13540   13698   +158     
+ Misses       6123    5965   -158     

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