Fix indentation and trailing commas

This will make the diffs introducing substative changes easier to read.
Consistent indenting and always having trailing commas on lists and
dictionaries makes for smaller diffs.

tests/app/test_utils.py

@@ -426,9 +426,9 @@ def test_get_letter_validation_error_for_unknown_error():
      'Letters must be 10 pages or less. <br>Your letter is 13 pages long.')
 ])
 def test_get_letter_validation_error_for_known_errors(
-        error_message,
-        expected_title,
-        expected_content,
+    error_message,
+    expected_title,
+    expected_content,
 ):
     error = get_letter_validation_error(error_message, invalid_pages=[2], page_count=13)