Revert "chore: remove test action"

This reverts commit fa434d61a5.

.forgejo/workflows/test.yaml

@@ -0,0 +1,24 @@
+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: direnv
+        run: direnv allow
+      - name: treefmt
+        run: |
+          echo "##[group]direnv/treefmt"
+          direnv allow
+          treefmt