Reset color cycle before tests.

We need to reset the color cycle for placeholders before each CSS property test because we need to ensure consistent colouring of the placeholders as tests are added/removed/reordered.

tests/snapshot_tests/test_snapshots.py

@@ -137,6 +137,7 @@ PATHS = [
 @pytest.mark.parametrize("file_name", PATHS)
 def test_css_property(file_name, snap_compare):
     path_to_app = STYLES_EXAMPLES_DIR / file_name
+    Placeholder.reset_color_cycle()
     assert snap_compare(path_to_app)