Integrate render tests into CI checks

[w23]

Roughly, this would entail setting up steam deck for running CI builds by GH triggers:

• [ ] install GH agent
• [ ] figure out how to secure it
• [ ] how to report results: need both numbers and easily-viewable visual/image results
  • [ ] upload to some hosting somewhere?
• [ ] how to mask known flaky tests (probably all of them are flaky)
• [ ] how to synchronize it with the PBR repo (updates there can lead to tests failing)