python,util: Fixed string decoding in include verifier

python,util: Fixed string decoding in include verifier

The Python2 <-> Python3 port included a decode on a string as part of
the include statement git-hook verifier. This results in a failure. To
fix this issue, the file to be checked is opened in binary mode.

This issue was highlighted by Gabe Black here:
https://gem5-review.googlesource.com/c/public/gem5/+/28588

Change-Id: I9a30ecc24d4741853ed1c2d0c03addf57c3e5b6c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30336
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>