`esmvalcore.cmor.table.read_cmor_tables()` does not restrict type of argument, consequently gets confused and kicks bucket

[valeriupredoi]

read_cmor_tables(cfg_developer: Optional[Path] = None) -> None: needs to restrict type of argument or check if argument is of type Path before doing anything - instead, it happily accepts cfg_developer of type Dict and crashes when getting stat() method, coz la-dee-dah Dict obejcts don't have stat() methods, see bkwards incompatible failed tests in ESMValTool