Switch to all-string raw values in .yaml for Django 4.0 compatibility (#165)

Author: nickmoreton

tests/templates/patterns/atoms/tags_test_atom/tags_test_atom.yaml

@@ -3,9 +3,9 @@ tags:
     empty_string:
       raw: ''
     none:
-      raw: null
+      raw: 'None'
     zero:
-      raw: 0
+      raw: '0'
   default_html_tag:
     page.url:
       raw: "example"
@@ -16,7 +16,7 @@ tags:
     empty_string:
       raw: ''
     none:
-      raw: null
+      raw: 'None'
     zero:
-      raw: 0
+      raw: '0'