requirements.txt: Update -f link for PyTorch CPU HTML page

[joshuacwnewton]

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Description

The link we're using currently throws a deprecation warning:

DEPRECATION: The HTML index page being used (https://download.pytorch.org/whl/cpu/torch_stable.html) is not a proper HTML 5 document. This is in violation of PEP 503 which requires these pages to be well-formed HTML 5 documents. Please reach out to the owners of this index page, and ask them to update this index page to a valid HTML 5 document. pip 22.2 will enforce this behaviour change. Discussion can be found at pypa/pip#10825

I've implemented the suggestion from: pytorch/pytorch#72180 (comment)

Linked issues

N/A

[codecov]

Codecov Report

Merging #3679 (d8a2224) into master (7e7d8a4) will not change coverage.
The diff coverage is n/a.

Flag	Coverage Δ
api-tests	24.20% <ø> (-0.26%)	⬇️
cli-tests	56.84% <ø> (ø)

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[mguaypaq]

Thanks for noticing, reporting to upstream, and finding the correct paths to use! LGTM