ci: merge scripts which install dependencies

We have two different scripts which install dependencies, one for
dockerized jobs and one for non-dockerized ones. Naturally, these
scripts have quite some duplication. Furthermore, either of these
scripts is missing some test dependencies that the respective other
script has, thus reducing test coverage.

Merge those two scripts such that there is a single source of truth for
test dependencies, only.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.github/workflows/main.yml

@@ -359,7 +359,7 @@ jobs:
       if: matrix.vector.jobname != 'linux32'
     - uses: actions/checkout@v1 # cannot be upgraded because Node.js Actions aren't supported in this container
       if: matrix.vector.jobname == 'linux32'
-    - run: ci/install-docker-dependencies.sh
+    - run: ci/install-dependencies.sh
     - run: ci/run-build-and-tests.sh
     - name: print test failures
       if: failure() && env.FAILED_TEST_ARTIFACTS != ''