add _dbm and _gdbm to align naming of error types with runtime (#12978)

stdlib/@tests/stubtest_allowlists/darwin.txt

@@ -18,6 +18,7 @@ select.POLLMSG   # system dependent
 (readline.append_history_file)?
 (fcntl.F_GETLEASE)?
 (fcntl.F_SETLEASE)?
+(_gdbm)?
 
 # Platform differences that cannot be captured by the type system
 (posix.O_[A-Z_]+)?

stdlib/@tests/stubtest_allowlists/win32.txt

@@ -18,6 +18,8 @@ _winapi.VirtualQuerySize
 
 # Modules that do not exist on Windows systems
 _curses
+_dbm
+_gdbm
 _posixsubprocess
 asyncio.unix_events
 dbm.gnu