Document `AStar.get_point_path()` not being thread-safe

(cherry picked from commit cf64bad63ec29369bada3b2cfed380da403a479a)

doc/classes/AStar.xml

@@ -224,6 +224,7 @@
 			</argument>
 			<description>
 				Returns an array with the points that are in the path found by AStar between the given points. The array is ordered from the starting point to the ending point of the path.
+				[b]Note:[/b] This method is not thread-safe. If called from a [Thread], it will return an empty [PoolVector3Array] and will print an error message.
 			</description>
 		</method>
 		<method name="get_point_position" qualifiers="const">

doc/classes/AStar2D.xml

@@ -206,6 +206,7 @@
 			</argument>
 			<description>
 				Returns an array with the points that are in the path found by AStar2D between the given points. The array is ordered from the starting point to the ending point of the path.
+				[b]Note:[/b] This method is not thread-safe. If called from a [Thread], it will return an empty [PoolVector2Array] and will print an error message.
 			</description>
 		</method>
 		<method name="get_point_position" qualifiers="const">