ci: add GitLab mirror workflow

Author: scuba10steve

.github/workflows/gitlab-mirror.yml

@@ -0,0 +1,19 @@
+name: GitLab Mirror
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  mirror:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7.0.0
+        with:
+          fetch-depth: 0
+
+      - name: Push to GitLab
+        run: |
+          git remote add gitlab "https://${{ secrets.GITLAB_MIRROR_USER }}:${{ secrets.GITLAB_MIRROR_TOKEN }}@gitlab.com/orchard-cde/github.git"
+          git push gitlab HEAD:main