qemu: Fix Python deps, the third time

Hooks from `python` (specifically the one that adds `pythonPath`) are needed by `python/scripts/mkvenv.py` to find meson

With `python.withPackages`

```
python determined to be '/nix/store/r98crvxg8pmrvx9vzymhlwbbvffnzjhl-python3-3.13.6-env/bin/python3'
python version: Python 3.13.6
mkvenv: Creating non-isolated virtual environment (with packages from '/nix/store/r98crvxg8pmrvx9vzymhlwbbvffnzjhl-python3-3.13.6-env/lib/python3.13/site-packages') at 'pyvenv'
mkvenv: checking for meson>=1.5.0
mkvenv: checking for pycotap>=1.1.0
mkvenv: installing meson==1.5.0, pycotap==1.3.1
```

With `pythonPackages.python`

```
python version: Python 3.13.6
mkvenv: Creating non-isolated virtual environment at 'pyvenv'
mkvenv: checking for meson>=1.5.0
mkvenv: checking for pycotap>=1.1.0
mkvenv: installing pycotap==1.3.1
```

Here's a diff of the env-vars https://gist.github.com/Artturin/e79f1fcf125ebb138c0012008e719533



the `withPackages` without `pythonOnBuildForHost` was wrong too but
changing it didn't fix the issue

Fixes this error in qemu-user / qemu minimal

```
$ ./result/bin/qemu-aarch64
./result/bin/qemu-aarch64: error while loading shared libraries: libz.so.1: cannot open shared object file: No such file or directory
```

Co-authored-by: dramforever <dramforever@live.com>