test: add test for networking setup in act (#1375)

* test: add test for networking setup in act

This test makes sure that the hostname inside of act is resolvable.

* fix: only merge existing container options

When merging parsed container options without options being
set in a job, the default docker options are returned and
will override the expected defaults by act (e.g. network mode).

This is a first attempt to mitigate this behavior and only
merge settings if something was requested on a job.

* refactor: split config merging into own function

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pkg/runner/testdata/networking/push.yml

@@ -0,0 +1,14 @@
+name: test network setup
+on: push
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install tools
+        run: |
+          apt update
+          apt install -y bind9-host
+      - name: Run hostname test
+        run: |
+          hostname -f
+          host $(hostname -f)