test-maximize: Restore old border width

When the border width changes, we move the client according to its
gravity. This can cause problems with the following code. Fix this by
restoring the original border width again, which undoes the move.

Signed-off-by: Uli Schlachter <psychon@znc.in>

tests/test-maximize.lua

@@ -75,6 +75,9 @@ local steps = {
 
         assert(c.border_width == test_width)
 
+        -- Restore old border width
+        c.border_width = test_width - 1
+
         return true
     end,