fix: don't add creation index if one exists (#26295) (#26297)

(cherry picked from commit f183a31)

Co-authored-by: Ankush Menat <ankush@frappe.io>

frappe/database/mariadb/schema.py

@@ -90,7 +90,7 @@ def alter(self):
 			if not frappe.db.get_column_index(self.table_name, col.fieldname, unique=False):
 				add_index_query.append(f"ADD INDEX `{col.fieldname}_index`(`{col.fieldname}`)")
 
-		if self.meta.sort_field == "creation" and frappe.db.get_column_index(
+		if self.meta.sort_field == "creation" and not frappe.db.get_column_index(
 			self.table_name, "creation", unique=False
 		):
 			add_index_query.append("ADD INDEX `creation`(`creation`)")