Fix App Push Test

[kamilzyla]

Changes

1. Fix our App Push Test using a workaround for issue in renv.
2. Add SHA to the commit messages generated by App Push Test, so the triggering commit can be easily identified just by looking at the list of workflow runs, even if the logs are no longer available.
3. Add a badge back to the README. (See discussion.)
4. Improve docs.

I have also regenerated the APP_PUSH_TEST_PAT (described in the docs); it will be good for another year.

How to test

See the workflow runs for App Push Test and the resulting Rhino Test (triggered manually for this branch).

[jakubnowicki]

Looks good, thank you for the fix. Please consider my comment in the README.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (091f967) 17.82% compared to head (ddd4df3) 17.82%.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #514   +/-   ##
=======================================
  Coverage   17.82%   17.82%           
=======================================
  Files           9        9           
  Lines         404      404           
=======================================
  Hits           72       72           
  Misses        332      332           

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