use mysql's default string length for mariadb

Author: itsbekas

sqlmodel/sql/sqltypes.py

@@ -14,7 +14,9 @@ class AutoString(types.TypeDecorator):  # type: ignore
 
     def load_dialect_impl(self, dialect: Dialect) -> "types.TypeEngine[Any]":
         impl = cast(types.String, self.impl)
-        if impl.length is None and dialect.name == "mysql":
+        if impl.length is None and (
+            dialect.name == "mysql" or dialect.name == "mariadb"
+        ):
             return dialect.type_descriptor(types.String(self.mysql_default_length))
         return super().load_dialect_impl(dialect)