asdf-python and pacman

Hey there,

I've been using this plugin since 2016 (!) and `asdf` is still by far my favourite version manager.

Since the start, I've had issues with asdf's python confusing applications which rely on the `system` python.

In my `~/.tool-versions`, I have my python setup like so:

```
python system 3.8.2 2.7.17
```

I understand that this line will try the system python first, then try 3.8.2, then 2.7.17.

When I reshim python, then trigger my AUR package updates, I get the following error:

```
asdf reshim python && yay -Syu
< SNIP >
copying aigpy/__main__.py -> build/lib/aigpy
running egg_info
writing requirements to aigpy.egg-info/requires.txt
writing aigpy.egg-info/PKG-INFO
writing top-level names to aigpy.egg-info/top_level.txt
writing dependency_links to aigpy.egg-info/dependency_links.txt
reading manifest file 'aigpy.egg-info/SOURCES.txt'
writing manifest file 'aigpy.egg-info/SOURCES.txt'
==> Entering fakeroot environment...
==> Starting package_python-aigpy()...
unknown command: python. Perhaps you have to reshim?
==> ERROR: A failure occurred in package_python-aigpy().
Aborting...
Error making: python-aigpy
```

Looking at the `python-aigpy` package, python is being called like so:

```
depends=(
'python2'
'python2-requests'
'python2-libconfigparser'
'python2-colorama'
'python2-mutagen'
'python2-futures'
)
cd "${srcdir}/${_pkgname}-${pkgver}-2"
python2 setup.py install --root="${pkgdir}/" --optimize=1 --skip-build
install -Dm644 "${srcdir}/LICENSE" "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE"
```

`which python2` points to `/home/john/.asdf/shims/python2`.

I'm not entirely sure where to go from here - how can I ensure that pacman installs packages with the system pythons?