ci/e2e-tests: streamline playwright tests (#1380)

Ubuntu's `man-db` package updates can cause significant slowdown in job setup.

As there's no need for manpages in CI builds, the offending package can be removed.

See:

* actions/runner#4030
* https://bugs.launchpad.net/ubuntu/+source/man-db/+bug/2073797
* getodk/central-backend#1642

Author: alxndrsn

.github/workflows/tests.yml

@@ -15,6 +15,12 @@ jobs:
     timeout-minutes: 120
     runs-on: ubuntu-latest
     steps:
+
+    # This one weird trick speeds up every build!
+    # see: https://github.com/getodk/central-backend/pull/1642
+    # see: https://github.com/actions/runner/issues/4030
+    - run: sudo apt-get remove --purge man-db
+
     - uses: actions/checkout@v4
       with:
         path: client