chore: add action for format checking

.forgejo/workflows/test.yaml

@@ -1,24 +0,0 @@
-name: Test some stuff
-
-on:
-  push:
-    branches:
-      - main
-    paths:
-      - .forgejo/workflows/test.yaml
-
-jobs:
-  test:
-    runs-on: nixos-latest
-    steps:
-      - name: checkout
-        uses: actions/checkout@v4
-        with:
-          ref: 'main'
-      - name: dev
-        uses: actions/nix/develop@main
-        with:
-          flake: .
-          run: |
-            direnv allow
-            treefmt