[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

gaphor/ui/tests/test_diagrampage.py

@@ -38,4 +38,4 @@ def test_placement_icon_base_is_loaded_once():
     icon1 = placement_icon_base()
     icon2 = placement_icon_base()
 
-    assert icon1 is icon2
+    assert icon1 is icon2