fix(test): screen:expect({none=…}) with no any/grid

Problem:
`screen:expect({none=…})` with no any/grid crashed (concat on nil)
because actual_rows was only rendered when any or grid was present.

Solution:
Update the condition.

test/functional/ui/screen.lua

@@ -551,7 +551,7 @@ function Screen:expect(expected, attr_ids, ...)
     end
 
     local actual_rows
-    if expected.any or grid then
+    if expected.any or expected.none or grid then
       actual_rows = self:render(not (expected.any or expected.none), attr_state)
     end