Python3 str vs bytes issue in `verifyarchives.py`

[jonasbardino]

We hit a classic str vs bytes issue when trying to verify Archive contents with the verifyarchives.py helper on python3:

su - mig -c 'PYTHONPATH=/home/mig mig/server/verifyarchives.py -A 1747555723 -I "*EMAIL_REDACTED*" -n "archive-OPQYzF"'
searching for Archives with creation stamp between 1747555723 and 1750230523
Archive integrity checks:
Could not open archive helpers /home/mig/state/freeze_home/USERID_REDACTED/archive-OPQYzF.cache and
/home/mig/state/freeze_home/USERHOME_REDACTED/archive-OPQYzF/meta.pck for verification:
a bytes-like object is required, not 'str'
/home/mig/state/freeze_home/USERHOME_REDACTED/archive-OPQYzF [FAIL]