[CI] push forgejo branches to the specified destination

(cherry picked from commit 22abd100cbab75673c53e4fb36fa574ada660aee)
(cherry picked from commit 4e2c30cb5bcd7a4e2b2385a774062492e741a9e9)
(cherry picked from commit 1ddc08747c8819e8967c95d54d3e273ef3831570)
(cherry picked from commit ba3df0131412c2eb41a3312558bc4df5881caad5)
(cherry picked from commit 644f7cb7338ae09b5ea7021132e93c70ba8fc771)

.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/*