Change "Return" to "Returns" where necessary in XML documentation

In many of the XML files it had been noted that when the documentation
refers to a return value, both "Return" and "Returns" are used. This
has now been fixed to only say "Returns".

Fixes #28867

doc/classes/EditorResourcePreviewGenerator.xml

@@ -57,7 +57,7 @@
 			<argument index="0" name="type" type="String">
 			</argument>
 			<description>
-				Return if your generator supports this resource type.
+				Returns if your generator supports this resource type.
 			</description>
 		</method>
 	</methods>