Fix sql with '' regexp issue in similar to

server/mergin/auth/models.py

@@ -204,21 +204,22 @@ def generate_username(cls, email: str) -> Optional[str]:
         # additional check for reserved words
         username = f"{username}0" if is_reserved_word(username) else username
         # check if we already do not have existing usernames
-        suffix = db.session.execute(
+        query = db.session.execute(
             text(
                 """
                 SELECT
                     replace(username, :username, '0')::int AS suffix
                 FROM "user"
                 WHERE
                     username = :username OR
-                    username SIMILAR TO :username'\d+'
+                    username SIMILAR TO :username_like
                 ORDER BY replace(username, :username, '0')::int DESC
                 LIMIT 1;
                 """
             ),
-            {"username": username},
-        ).scalar()
+            {"username": username, "username_like": f"{username}\d+"},
+        )
+        suffix = query.scalar()
         return username if suffix is None else username + str(int(suffix) + 1)
 
     @classmethod