stdlib: Remove final decorator from abstract board

@typing.final was not introduced until python3.8.

Change-Id: I65a5f4b5655d2ad80f7b566f9cea8e2371b3be62
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55863
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/gem5/components/boards/abstract_board.py

@@ -37,7 +37,7 @@ from m5.objects import (
     VoltageDomain,
 )
 
-from typing import List, final
+from typing import List
 
 
 class AbstractBoard(System):
@@ -236,7 +236,6 @@ class AbstractBoard(System):
         """
         raise NotImplementedError
 
-    @final
     def _connect_things(self) -> None:
         """Connects all the components to the board.