Improve mysql instance label value. (#14827)

content/en/docs/concepts/overview/working-with-objects/common-labels.md

@@ -144,7 +144,7 @@ kind: StatefulSet
 metadata:
   labels:
     app.kubernetes.io/name: mysql
-    app.kubernetes.io/instance: wordpress-abcxzy
+    app.kubernetes.io/instance: mysql-abcxzy
     app.kubernetes.io/managed-by: helm
     app.kubernetes.io/component: database
     app.kubernetes.io/part-of: wordpress
@@ -160,7 +160,7 @@ kind: Service
 metadata:
   labels:
     app.kubernetes.io/name: mysql
-    app.kubernetes.io/instance: wordpress-abcxzy
+    app.kubernetes.io/instance: mysql-abcxzy
     app.kubernetes.io/managed-by: helm
     app.kubernetes.io/component: database
     app.kubernetes.io/part-of: wordpress
@@ -170,4 +170,4 @@ metadata:
 
 With the MySQL `StatefulSet` and `Service` you'll notice information about both MySQL and Wordpress, the broader application, are included.
 
-{{% /capture %}}
+{{% /capture %}}