Bump utils to improve plain text email formatting

Brings in:
- [x] https://github.com/alphagov/notifications-utils/pull/438
- [x] https://github.com/alphagov/notifications-utils/pull/450
- [x] https://github.com/alphagov/notifications-utils/pull/454

Changes:
- https://github.com/alphagov/notifications-utils/compare/25.3.0...26.2.0

tests/app/v2/notifications/test_get_notifications.py

@@ -120,7 +120,7 @@ def test_get_notification_by_id_with_placeholders_returns_200(
         'status': '{}'.format(sample_notification.status),
         'template': expected_template_response,
         'created_at': sample_notification.created_at.strftime(DATETIME_FORMAT),
-        'body': "Hello Bob\nThis is an email from GOV.\u200bUK",
+        'body': "Hello Bob\nThis is an email from GOV.UK",
         "subject": "Bob",
         'sent_at': sample_notification.sent_at,
         'completed_at': sample_notification.completed_at(),

tests/app/v2/notifications/test_post_notifications.py

@@ -313,7 +313,7 @@ def test_post_email_notification_returns_201(client, sample_email_template_with_
     assert notification.reference is None
     assert notification.reply_to_text is None
     assert resp_json['content']['body'] == sample_email_template_with_placeholders.content \
-        .replace('((name))', 'Bob').replace('GOV.UK', u'GOV.\u200bUK')
+        .replace('((name))', 'Bob')
     assert resp_json['content']['subject'] == sample_email_template_with_placeholders.subject \
         .replace('((name))', 'Bob')
     assert resp_json['content']['from_email'] == "{}@{}".format(