Add build workflow for Archlinux package

.forgejo/workflows/build.yaml

@@ -0,0 +1,28 @@
+name: Build and push Archlinux package
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+
+jobs:
+  build:
+    runs-on: archlinux
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Build package
+        run: |
+          cp PKGBUILD /tmp
+          pushd /tmp
+          makepkg -fC --syncdeps --noconfirm
+          popd
+          cp /tmp/*.pkg.tar.zst package.pkg.tar.zst
+      - name: Push package
+        run: |
+          curl -X PUT \
+            ${{ github.server_url }}/api/packages/${{ github.repository_owner }}/arch/os \
+            --user ${{ vars.DOCKER_PUSH_USERNAME }}:${{ secrets.DOCKER_PUSH_PASSWORD }} \
+            --header "Content-Type: application/octet-stream" \
+            --data-binary '@./package.pkg.tar.zst'