[CI] push forgejo branches to the specified destination

.forgejo/workflows/mirror.yml

@@ -0,0 +1,25 @@
+name: mirror
+
+on:
+  push:
+    branches:
+      - 'forgejo'
+      - 'v*/forgejo'
+
+jobs:
+  mirror:
+    if: ${{ secrets.MIRROR_TOKEN != '' }}
+    runs-on: docker
+    container:
+      image: 'docker.io/node:20-bookworm'
+    steps:
+      - name: git push {v*/,}forgejo
+        run: |
+          git init --bare .
+          git remote add origin ${{ env.GITHUB_SERVER_URL }}/${{ env.GITHUB_REPOSITORY }}
+          git fetch origin refs/heads/forgejo:refs/mirror/forgejo
+          git ls-remote origin refs/heads/v*/forgejo | while read sha full_ref ; do
+            ref=${full_ref#refs/heads/}
+            git fetch origin $full_ref:refs/mirror/$ref
+          done
+          git push --force https://any:${{ secrets.MIRROR_TOKEN }}@${{ vars.MIRROR_DESTINATION }} refs/mirror/*:refs/heads/*