Add automatic deploy to vercel preview in the workflow that tests pull requests

[svogt0511]

Currently when committing code that is part of a pull request, the test suite is run and then the workflow stops. Since quite often I want a vercel preview, as well, I have to run the 'Manually Test and Deploy Branch to Vercel' workflow which runs the test suite again before deploying. This means I have to run the test suite twice to get a vercel preview. The test suite takes about 20 minutes to run, which means it takes about 40 minutes to get a preview. This will cut the time-to-preview in half.