pkg_zip creates the zip file with broken link inside venv

Using latest rules_python 1.8.2 (venv enabled) and rules_pkg 1.2.0

```
py_binary(
name = "app",
...
)

pkg_zip(
name = "app_zip",
srcs = [":app"],
include_runfiles = True,
)
```

When I unzip the app_zip.zip file, I can see all the symlinks inside app.runfiles/_main/utils/_app.venv are broken. They all have one extra ../

I checked unzipped directory structure, those rules_python++pip* directories are wrongly located inside app.runfiles/_main/ while on the build host bazel-bin, they are directly inside app.runfiles, parallel to _main. This caused all symlinks in venv broken.