CI: add workflow to sync master to current automatically (#77)

Signed-off-by: Jinzhe Zeng <[email protected]>

.gitattributes

@@ -1 +1,3 @@
 .git_archival.txt  export-subst
+# different in different branches
+.nvmrc merge=ours

.github/workflows/sync-branch.yml

@@ -0,0 +1,53 @@
+name: Sync master to current
+
+on:
+  push:
+    branches:
+      - master
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
+  cancel-in-progress: true
+
+permissions:
+  pull-requests: write
+  contents: write
+
+jobs:
+  pr:
+    name: Submit PR
+    runs-on: ubuntu-latest
+    env:
+      target_branch: current
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ env.target_branch }}
+          fetch-depth: 0
+      - name: Create PR
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git branch ${BRANCH_NAME} -f
+          git checkout ${BRANCH_NAME}
+          git config --global merge.ours.driver true
+          # sync .gitattributes first
+          git checkout origin/${{ github.ref_name }} -- .gitattributes
+          git add .gitattributes
+          if git diff-index --quiet HEAD --; then
+              echo "No changes to commit."
+          else
+              git commit -m "Sync .gitattributes from ${{ github.ref_name }}"
+          fi
+          git merge origin/${{ github.ref_name }}
+          git push origin ${BRANCH_NAME} --force
+          PR_URL="$(gh pr list --head "${BRANCH_NAME}" --state open --json url --jq .[].url)"
+          if [[ -n "${PR_URL}" ]]; then
+              echo "PR already exists -> ${PR_URL}"
+              exit 0
+          else
+              gh pr create --title "Sync ${{ github.ref_name }} to ${{ env.target_branch }}" --body "Generated by GitHub Actions" --base ${{ env.target_branch }} -r njzjz -a njzjz
+          fi
+        env:
+          GH_TOKEN: ${{ github.token }}
+          BRANCH_NAME: sync-branches/${{ github.ref_name }}-to-${{ env.target_branch }}