ci(forgejo): support alpine runner image

.gitea/workflows/build.yaml

@@ -18,10 +18,15 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Install Docker CLI
+      - name: Install tooling
         run: |
-          apt-get update
+          set -euo pipefail
-          apt-get install -y docker.io git python3
+          if command -v apt-get >/dev/null 2>&1; then
+            apt-get update
+            apt-get install -y docker.io git python3
+          elif command -v apk >/dev/null 2>&1; then
+            apk add --no-cache git python3 py3-pip
+          fi
 
       - name: Log in to registry
         run: |