hash_password: raise an error if no config file is specified (#12789)

changelog.d/12789.misc

@@ -0,0 +1 @@
+The `hash_password` script now fails when it is called without specifying a config file.

synapse/_scripts/hash_password.py

@@ -46,10 +46,10 @@ def main() -> None:
             "Path to server config file. "
             "Used to read in bcrypt_rounds and password_pepper."
         ),
+        required=True,
     )
 
     args = parser.parse_args()
-    if "config" in args and args.config:
     config = yaml.safe_load(args.config)
     bcrypt_rounds = config.get("bcrypt_rounds", bcrypt_rounds)
     password_config = config.get("password_config", None) or {}