Fix incorrect reference image used by previously broken test

Author: nyalldawson

tests/src/python/test_qgssinglesymbolrenderer.py

@@ -81,8 +81,8 @@ def testOrderBy(self):
         self.renderer.setOrderByEnabled(False)
         self.assertTrue(
             self.render_map_settings_check(
-                'single',
-                'single',
+                'singlesymbol_noorderby',
+                'singlesymbol_noorderby',
                 self.mapsettings)
         )