Fix documentation with misleading data type (#78157)

##### SUMMARY
The sample value given for the 'mode' parameter is shown without quotes, but the data type is string. If you actually try to use an unquoted numeric string for this value you're in for a nasty surprise! I added quotation marks to the sample value.
##### ISSUE TYPE
- Docs Pull Request

+label: docsite_pr

lib/ansible/modules/copy.py

@@ -268,7 +268,7 @@ mode:
     description: Permissions of the target, after execution.
     returned: success
     type: str
-    sample: 0644
+    sample: "0644"
 size:
     description: Size of the target, after execution.
     returned: success