`atypes` not defined in python `inline`

### Problem
`beet fields` lists `albumtype`, `albumtypes`, and `atypes` as available tags.

`albumtype` and `albumtypes`, are well and usable within the `inline` python script, however, `atypes` is not, and crashes with:

```
NameError: name 'atypes' is not defined
```

example:

```yaml
album_fields:
test: |
import platform
log = open("log.txt", "a")
log.write("type:" + albumtype + '\n') // ok
log.write("types:" + albumtypes + '\n') // ok
log.write("atypes:" + atypes + '\n') // NameError: name 'atypes' is not defined
```
I have tried using it first e.g.

```yaml
paths:
default: ${atypes}${test}/...
```
just to see if it makes a difference, but no go.

`${atypes}` itself in path does work completely fine.

I don't know if this is intentional, but it would be nice to be able to use the renamed values, e.g. `compilation: Anthology` / `dj-mix: DJ-Mix` inline without doing a match.

### Setup

* OS: Debian
beets version 1.6.0
Python version 3.9.2
plugins: albumtypes, bandcamp, chroma, copyartifacts, discogs, edit, fromfilename, inline, lastgenre, the
* Turning off plugins made problem go away (yes/no): N/A

My configuration (output of `beet config`) is:

Click to expand

```yaml
directory: ~/data/user/gremious/public/beets_music
library: ~/data/user/gremious/public/beets_music/library.db

plugins: albumtypes fromfilename inline discogs chroma copyartifacts lastgenre bandcamp edit the
languages: en
per_disc_numbering: yes
chroma:
auto: yes
copyartifacts:
print_ignored: yes
extensions: .*
lastgenre:
count: 99
force: no
whitelist: yes
min_weight: 10
fallback:
canonical: no
source: album
auto: yes
separator: ', '
prefer_specific: no
title_case: yes
albumtypes:
types:
- album: Album
- ep: EP
- single: Single
- soundtrack: OST
- remix: Remix
- live: Live
- mixtape: Mixtape
- compilation: Compilation
- dj-mix: DJ-Mix
- demo: Demo
- other: Other
ignore_va: ''
bracket: ' '

album_fields:
test: "import platform\nlog = open(\"log.txt\", \"a\")\nlog.write(\"type:\" + albumtype + '\\n')\nlog.write(\"types:\" + albumtypes + '\\n')\nlog.write(\"atypes:\" + atypes + '\\n')\n\nret = \"\"\ntypes = albumtypes.split(' ')\n\nif len(types) <= 1:\n return albumtypes\n\n# if types[0] == \"Album\":\n # types.pop(0)\n # return types\n# else:\n # return albumtypes\n"

paths:
default: ${albumartist}/${atypes}$album/${track}. $title
comp: ${test}/${track}. $title
singleton: Misc Tracks/${artist} - ${title}
albumtype:soundtrack: Soundtracks/${albumartist} - ${album}/${track}. $artist - $title
discogs:
apikey: REDACTED
apisecret: REDACTED
tokenfile: discogs_token.json
source_weight: 0.5
user_token: REDACTED
separator: ', '
index_tracks: no
edit:
albumfields: album albumartist
itemfields: track title artist album
ignore_fields: id path
the:
the: yes
a: yes
format: '{0}, {1}'
strip: no
patterns: []
bandcamp:
include_digital_only_tracks: yes
search_max: 2
art: no
exclude_extra_fields: []
genre:
capitalize: no
maximum: 0
mode: progressive
always_include: []
comments_separator: '

---

'
pathfields: {}
item_fields: {}
```