Tidy garbage collection controller page (#14856)

* Tidy code blocks

* Reword for better readability

content/en/docs/concepts/workloads/controllers/garbage-collection.md

@@ -45,7 +45,7 @@ kubectl get pods --output=yaml
 
 The output shows that the Pod owner is a ReplicaSet named `my-repset`:
 
-```shell
+```yaml
 apiVersion: v1
 kind: Pod
 metadata:
@@ -61,7 +61,7 @@ metadata:
 ```
 
 {{< note >}}
-Cross-namespace owner references is disallowed by design. This means: 
+Cross-namespace owner references are disallowed by design. This means:
 1) Namespace-scoped dependents can only specify owners in the same namespace,
 and owners that are cluster-scoped.
 2) Cluster-scoped dependents can only specify cluster-scoped owners, but not