chore(ci): run CI in an archlinux image

We can assume mores tools a present, and should be able to mock less
(e.g. we can remove the `vercmp` mock next).

Author: pbrisbin

.github/workflows/ci.yml

@@ -8,12 +8,15 @@ jobs:
   test:
     runs-on: ubuntu-latest
 
+    container:
+      image: "archlinux:base-devel"
+
     env:
       FIXTURES_NO_RECORD: 1
 
     steps:
       - uses: actions/checkout@v6
-      - uses: actions/setup-python@v5
-      - run: pip install cram
-      - uses: extractions/setup-just@v2
-      - run: just test
+      - run: pacman -Sy --needed --noconfirm just python-cram
+      - run: |
+          useradd ci
+          runuser -u ci -- just test