docs: Add GitHub Releases page to project url metadata

[matthewfeickert]

Description

Add https://github.com/scikit-hep/pyhf/releases to 'Project links' section on PyPI webpage.

Inspired by Awkward's use, which was added in scikit-hep/awkward@0a80b2a.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Add https://github.com/scikit-hep/pyhf/releases to 'Project links' section
  on PyPI webpage.

[codecov]

Codecov Report

Base: 98.30% // Head: 98.30% // No change to project coverage 👍

Coverage data is based on head (d5d8703) compared to base (e942d85).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2099   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files          69       69           
  Lines        4531     4531           
  Branches      645      645           
=======================================
  Hits         4454     4454           
  Misses         45       45           
  Partials       32       32           

Flag	Coverage Δ
contrib	97.88% <ø> (ø)
doctest	61.15% <ø> (ø)
unittests-3.10	96.31% <ø> (ø)
unittests-3.8	96.33% <ø> (ø)
unittests-3.9	96.35% <ø> (ø)

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