add guix installer workflow

.forgejo/workflows/installer.yaml

@@ -0,0 +1,32 @@
+# title: install
+# desc: generate a guix installer image
+# adapted from https://github.com/SystemCrafters/guix-installer/
+
+name: installer
+on: [push]
+jobs:
+  build:
+    runs-on: docker
+    container:
+      image: g.freya.cat/freya/guix:latest
+    steps:
+      - name: Git checkout
+        uses: actions/checkout@v4
+
+      - name: Guix cache
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/guix
+          key: guix-cache-${{ github.sha }}
+          restore-keys: |
+            guix-cache
+
+      - name: Build ISO
+        run: |
+          ./scripts/build-installer
+
+      - name: Save artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: installer
+          path: guix-installer-*.iso