Test install scripts with every merge

[gonuke]

With #1477 we created a workflow to test a standard installation script within this repo.

Currently, he conditions under which that script runs are too limiting:

  push:
    paths:
      - 'scripts/ubuntu.sh'
      - '.github/workflows/install_script.yml'

I think this test should run on every push to develop and on every pull_request to develop. By doing it on pull_request it will provide early insight to contributors that the installation is broken, but may also place too much burden on them. We can revisit this after some time.