Fix for PCC error with float16 tensor

[shenoynikhil]

What does this PR do?

Fixes #1813.

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📚 Documentation preview 📚: https://torchmetrics--1819.org.readthedocs.build/en/1819/

[Borda]

Can we pls add test covering this case?

[SkafteNicki]

Can we pls add test covering this case?

We do explicitly test that it does not work for float16:

torchmetrics/tests/unittests/regression/test_pearson.py

Lines 104 to 108 in 5a01f34

	@pytest.mark.xfail(reason="PearsonCorrCoef metric does not support cpu + half precision")
	def test_pearson_corrcoef_half_cpu(self, preds, target):
	"""Test dtype support of the metric on CPU."""
	num_outputs = EXTRA_DIM if preds.ndim == 3 else 1
	self.run_precision_test_cpu(preds, target, partial(PearsonCorrCoef, num_outputs=num_outputs), pearson_corrcoef)

So just removing the xfail should be enough.

[codecov]

Codecov Report

Merging #1819 (a20fb29) into master (c03a716) will decrease coverage by 47%.
The diff coverage is 100%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1819     +/-   ##
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- Coverage      87%     41%    -47%     
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  Files         254     254             
  Lines       14303   14306      +3     
========================================
- Hits        12510    5795   -6715     
- Misses       1793    8511   +6718