Fix Material.render_priority doc: no opaque sort

Opaque objects are rendered using the depth buffer, so the end result
appears sorted, but the opaque objects themselves are not sorted.

(cherry picked from commit 608bc8f3dc91930a7d1fc853e6fd8059434de973)

doc/classes/Material.xml

@@ -17,7 +17,7 @@
 		</member>
 		<member name="render_priority" type="int" setter="set_render_priority" getter="get_render_priority" default="0">
 			Sets the render priority for transparent objects in 3D scenes. Higher priority objects will be sorted in front of lower priority objects.
-			[b]Note:[/b] this only applies to sorting of transparent objects. This will not impact how transparent objects are sorted relative to opaque objects. This is because opaque objects are sorted based on depth, while transparent objects are sorted from back to front (subject to priority).
+			[b]Note:[/b] this only applies to sorting of transparent objects. This will not impact how transparent objects are sorted relative to opaque objects. This is because opaque objects are not sorted, while transparent objects are sorted from back to front (subject to priority).
 		</member>
 	</members>
 	<constants>