Run more of the tests on every pull request #6

Pull requests only run some of the tests. .github/workflows/build.yml runs t1, t3, t10, t11, t12, t13 and t14, but not t2, t4, t5, t6, t8 or t9, so a change could break those without anyone noticing until later. All 13 pass on a Mac.

Source code/tests/README.md warns that t4, t5 and t6 need a real network card, so some may not work on GitHub's build machines.

Done when: every test that can run reliably on GitHub's machines runs on each pull request, and any left out has a short comment saying why. Please run the workflow a few times, as a test that sometimes fails is worse than a missing one.