Fix templating + assertion on template validation

src/Runner.Worker/ActionManifestManager.cs

@@ -371,7 +371,7 @@ namespace GitHub.Runner.Worker
                         // stepsToken = run.Value.AssertMapping("steps");
                         // Maybe insert a for loop here instead since MappingToken is not supposed to be used in HandlerFactory.cs
                         // Just support 1 layer of steps w/ just run
-                        var steps = run.Value.AssertMapping("steps");
+                        var steps = run.Value.AssertSequence("steps");
                         // foreach (var s in steps) {
                         //     // Create list of steps
                         //     loadS

src/Runner.Worker/action_yaml.json

@@ -98,7 +98,16 @@
             }
         },
         "steps-item": {
-            "run-step": "non-empty-string"
+            "one-of": [
+                "run-step"
+            ]
+        },
+        "run-step": {
+            "mapping": {
+              "properties": {
+                "run": "non-empty-string"
+              }
+            }
         },
         "container-runs-context": {
             "context": [