[GH Actions] Include actions/setup-python action when using pip

Summary:
Another attempt to address https://linear.app/comm/issue/ENG-7606/fix-node-gyp-step-failing-on-github-ci

It appears that the fix works for image version 20240325.1, but NOT for image version 20240116.1. Which image version gets selected appears random. This should ensure that python command is reliably available.

Test Plan: Land and see what happens.

Reviewers: ashoat, ginsu, tomek, varun

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D11478