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

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