fix: reusable workflow panic (#1728)

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

pkg/model/workflow.go

@@ -123,7 +123,8 @@ type WorkflowCallResult struct {
 
 func (w *Workflow) WorkflowCallConfig() *WorkflowCall {
 	if w.RawOn.Kind != yaml.MappingNode {
-		return nil
+		// The callers expect for "on: workflow_call" and "on: [ workflow_call ]" a non nil return value
+		return &WorkflowCall{}
 	}
 
 	var val map[string]yaml.Node

pkg/runner/testdata/.github/workflows/local-reusable-workflow-no-inputs-array.yml

@@ -0,0 +1,10 @@
+name: reusable
+
+on:
+- workflow_call
+
+jobs:
+  reusable_workflow_job:
+    runs-on: ubuntu-latest
+    steps:
+    - run: echo Test

pkg/runner/testdata/.github/workflows/local-reusable-workflow-no-inputs-string.yml

@@ -0,0 +1,9 @@
+name: reusable
+
+on: workflow_call
+
+jobs:
+  reusable_workflow_job:
+    runs-on: ubuntu-latest
+    steps:
+    - run: echo Test

pkg/runner/testdata/uses-workflow/local-workflow.yml

@@ -19,6 +19,12 @@ jobs:
       number_required: 1
     secrets: inherit
 
+  reusable-workflow-with-on-string-notation:
+    uses: ./.github/workflows/local-reusable-workflow-no-inputs-string.yml
+
+  reusable-workflow-with-on-array-notation:
+    uses: ./.github/workflows/local-reusable-workflow-no-inputs-array.yml
+
   output-test:
     runs-on: ubuntu-latest
     needs: