revert explicit str concat

Author: invalidarg

pandas/tests/io/formats/style/test_style.py

@@ -895,8 +895,10 @@ def test_maybe_convert_css_to_tuples(self):
         assert maybe_convert_css_to_tuples("a:;c: ") == expected
 
     def test_maybe_convert_css_to_tuples_err(self):
-        msg = "Styles supplied as string must follow CSS rule formats, " \
-          "for example 'attr: val;'. 'err' was given."
+        msg = (
+            "Styles supplied as string must follow CSS rule formats, "
+            "for example 'attr: val;'. 'err' was given."
+        )
         with pytest.raises(ValueError, match=msg):
             maybe_convert_css_to_tuples("err")