Re-add yamllint stage to ci test manifest pipeline

Was accidentally removed in previous commit.

ci-test-manifest.yml

@@ -65,6 +65,14 @@ retrigger:
         ;
       done
 
+
+# --------------------------------------------------------------------------------------
+# Stage: infrastructure
+# --------------------------------------------------------------------------------------
+yamllint:
+  extends: .yamllint
+
+
 # --------------------------------------------------------------------------------------
 # Stage: build
 # --------------------------------------------------------------------------------------