Revert PyPy pin in GHA workflow

[blnicho]

Summary/Motivation:

In #3899 we added a temporary pin to the PyPy version we use for testing to work around issues in the 7.3.21 release. PyPy 7.3.22 is out now so this PR reverts the pin.

Changes proposed in this PR:

• Remove PyPy pin to make sure we're testing the latest version

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[blnicho]

Seems like PyPy 7.3.22 isn't yet available in the GHA runners (it's still installing 7.3.21 as of 5/1) so converting this to a draft for now.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.98%. Comparing base (c1ce36d) to head (3af792f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3925      +/-   ##
==========================================
- Coverage   89.98%   89.98%   -0.01%     
==========================================
  Files         904      904              
  Lines      106891   106891              
==========================================
- Hits        96191    96190       -1     
- Misses      10700    10701       +1     

Flag	Coverage Δ
builders	29.16% <ø> (+<0.01%)	⬆️
default	86.31% <ø> (?)
expensive	35.59% <ø> (?)
linux	87.45% <ø> (-2.04%)	⬇️
linux_other	87.45% <ø> (-0.01%)	⬇️
oldsolvers	28.09% <ø> (+<0.01%)	⬆️
osx	82.82% <ø> (ø)
win	85.88% <ø> (-0.01%)	⬇️
win_other	85.88% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.