[python] pin python package versions

CI failures in the opentitan repo were manifesting due to package
installation issues. This fixed the issues.

Signed-off-by: Tim Trippel <ttrippel@google.com>

requirements.txt

@@ -2,7 +2,6 @@
 # Licensed under the Apache License, Version 2.0, see LICENSE for details.
 # SPDX-License-Identifier: Apache-2.0
 
-hjson
-tabulate
-yapf
-
+hjson==3.1.0
+tabulate==0.8.10
+yapf==0.32.0