fix missing "s" in Viewport docs

(cherry picked from commit 63456bdd8ac9925b894ad33f99916d02b2c3d2b5)

doc/classes/Viewport.xml

@@ -252,7 +252,7 @@
 			The global canvas transform of the viewport. The canvas transform is relative to this.
 		</member>
 		<member name="gui_disable_input" type="bool" setter="set_disable_input" getter="is_input_disabled" default="false">
-			If [code]true[/code], the viewport will not receive input event.
+			If [code]true[/code], the viewport will not receive input events.
 		</member>
 		<member name="gui_snap_controls_to_pixels" type="bool" setter="set_snap_controls_to_pixels" getter="is_snap_controls_to_pixels_enabled" default="true">
 			If [code]true[/code], the GUI controls on the viewport will lay pixel perfectly.