fix: Check if `data-is-group` should be `true` before getting doc

frappe/core/doctype/user/user.py

@@ -1018,7 +1018,7 @@ def extract_mentions(txt):
 	soup = BeautifulSoup(txt, 'html.parser')
 	emails = []
 	for mention in soup.find_all(class_='mention'):
-		if mention.get('data-is-group'):
+		if mention.get('data-is-group') == 'true':
 			try:
 				user_group = frappe.get_cached_doc('User Group', mention['data-id'])
 				emails += [d.user for d in user_group.user_group_members]