Fix bug with attachments being pruned due to case/whitespace sensitivity

app/models/template_attachment.py

@@ -2,10 +2,16 @@
 import json
 
 from notifications_utils.insensitive_dict import InsensitiveDict
+from notifications_utils.insensitive_dict import InsensitiveSet as UtilsInsensitiveSet
 
 from app.extensions import redis_client
 from app.models import JSONModel
 
+# Implements https://github.com/alphagov/notifications-utils/pull/1197/files
+class InsensitiveSet(UtilsInsensitiveSet):
+    def __contains__(self, key):
+        return key in InsensitiveDict.from_keys(self)
+
 
 class TemplateAttachment(JSONModel):
     file_name: str
@@ -63,7 +69,7 @@ def __delitem__(self, placeholder_name):
     @property
     def count(self):
         return sum(
-            bool(self[key]) for key in self._dict if key in InsensitiveDict.from_keys(self._template.all_placeholders)
+            bool(self[key]) for key in self._dict if key in InsensitiveSet(self._template.all_placeholders)
         )
 
     @property
@@ -77,5 +83,5 @@ def as_personalisation(self):
 
     def prune_orphans(self):
         for placeholder in self._dict.keys():
-            if placeholder not in self._template.all_placeholders:
+            if placeholder not in InsensitiveSet(self._template.all_placeholders):
                 del self[placeholder]