test: make sure workflow_call is not a github event calling our workflow (#1520)

Since reusable workflows are defining inputs and ouputs using the
on.workflow_call syntax, this could also be triggered by a workflow_call
event. That event does not exist within GitHub and we should make
sure our worklow is not called by that kind of 'synthetic' event.

See https://github.com/nektos/act/pull/1423/files/74da5b085c0c4d08c5e5bf53501e555cb585b26c#r1042413431

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

Author: KnisterPeter

Diff for: pkg/runner/testdata/.github/workflows/local-reusable-workflow.yml

@@ -68,6 +68,11 @@ jobs:
         echo secrets.secret=${{ secrets.secret }}
         [[ "${{ secrets.secret == 'keep_it_private' }}" = "true" ]] || exit 1
 
+    - name: test github.event_name is never workflow_call
+      run: |
+        echo github.event_name=${{ github.event_name }}
+        [[ "${{ github.event_name != 'workflow_call' }}" = "true" ]] || exit 1
+
     - name: test output
       id: output_test
       run: |