add self-test workflow

tests/manifests/test-deployment.yaml

@@ -0,0 +1,19 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: pipeline-actions-test
+  namespace: pipeline-actions-test
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: pipeline-actions-test
+  template:
+    metadata:
+      labels:
+        app: pipeline-actions-test
+    spec:
+      containers:
+      - name: alpine
+        image: alpine:3.20
+        command: ["sleep", "3600"]

tests/manifests/test-namespace.yaml

@@ -0,0 +1,4 @@
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: pipeline-actions-test