Fix `matchLabelKeys` example yaml syntax

It should be `spec.template.spec.affinity` instead of `spec.template.affinity`.

```
$ explain deploy.spec.template.spec.affinity
GROUP:      apps
KIND:       Deployment
VERSION:    v1

FIELD: affinity <Affinity>

...
```
```
$ k explain deploy.spec.template.affinity
GROUP:      apps
KIND:       Deployment
VERSION:    v1

error: field "affinity" does not exist
```

content/en/docs/concepts/scheduling-eviction/assign-pod-node.md

@@ -391,21 +391,22 @@ metadata:
 ...
 spec:
   template:
-    affinity:
+    spec:
-      podAffinity:
+      affinity:
-        requiredDuringSchedulingIgnoredDuringExecution:
+        podAffinity:
-        - labelSelector:
+          requiredDuringSchedulingIgnoredDuringExecution:
-            matchExpressions:
+          - labelSelector:
-            - key: app
+              matchExpressions:
-              operator: In
+              - key: app
-              values:
+                operator: In
-              - database
+                values:
-          topologyKey: topology.kubernetes.io/zone
+                - database
-          # Only Pods from a given rollout are taken into consideration when calculating pod affinity.
+            topologyKey: topology.kubernetes.io/zone
-          # If you update the Deployment, the replacement Pods follow their own affinity rules
+            # Only Pods from a given rollout are taken into consideration when calculating pod affinity.
-          # (if there are any defined in the new Pod template)
+            # If you update the Deployment, the replacement Pods follow their own affinity rules
-          matchLabelKeys: 
+            # (if there are any defined in the new Pod template)
-          - pod-template-hash
+            matchLabelKeys: 
+            - pod-template-hash
 ```
 
 #### mismatchLabelKeys