Update nox-all CI job (frequenz-floss#138)

Author: Marenz

.github/workflows/ci.yaml

@@ -88,10 +88,14 @@ jobs:
     # The job name should match the name of the `nox` job.
     name: Test with nox
     needs: ["nox"]
+    # We skip this job only if nox was also skipped
+    if: always() && needs.nox.result != 'skipped'
     runs-on: ubuntu-20.04
+    env:
+      DEPS_RESULT: ${{ needs.nox.result }}
     steps:
-      - name: Return true
-        run: "true"
+      - name: Check matrix job result
+        run: test "$DEPS_RESULT" = "success"
 
   nox-cross-arch:
     name: Cross-arch tests with nox