Re-add PHP 7.4 and PostgreSQL tests to CI workflow

[geerlingguy]

Issue Type

• Feature Idea

Summary

Travis CI threw a wrench in our CI testing, so in #2109 I worked on moving from Travis CI to GitHub Actions (and dumping my old build scripts for Molecule, which does all the environment setup/teardown for me).

As part of that process, I disabled the custom PHP 7.4 and PostgreSQL tests, just for time reasons.

It should be simple enough to get them both working again, maybe by splitting out a separate playbook from the converge.yml playbook (and also adding a conditional in the verify.yml playbook so it doesn't test the extras like Varnish and Adminer...).