treat streets:streetlamp_basic_top_* as a type of post

as far as sign placement is concerned.

api.lua

@@ -649,6 +649,7 @@ function signs_lib.check_for_pole(pos, pointed_thing)
 		  or string.find(pnode.name, "default:fence_")
 		  or string.find(pnode.name, "_post")
 		  or string.find(pnode.name, "fencepost")
+		  or string.find(pnode.name, "streets:streetlamp_basic_top")
 		  or (pnode.name == "streets:bigpole" and pnode.param2 < 4)
 		  or (pnode.name == "streets:bigpole" and pnode.param2 > 19 and pnode.param2 < 24)
 		)