Run tests on OpenQA

[deeplow]

We'll also want to be able to test client PRs. Most likely we could just re-use the workstation openqa github workflow similar to this:

name: CI
on: [push]

jobs:
  openqa:
    runs-on: ubuntu-latest
    uses: freedomofpress/securedrop-workstation/.github/workflows/openqa.yml
    secrets: inherit
    needs: [check-openqa]

Other observations:

• There is already a try-client-pr make target in the workstation, which could be useful.
• workstation PR dependencies - often times client PRs are tested in tandem with