gh-99370: Calculate zip path from prefix when in a venv (GH-99371)

Before python3.11, when in a venv the zip path is calculated
from prefix on POSIX platforms. In python3.11 the behavior is
accidentally changed to calculating from default prefix. This
change will break venv created from a non-installed python
with a stdlib zip file. This commit restores the behavior back
to before python3.11.