Sync reference even if there are conflicts. (#16364)

Right now when there are conflicts between the language-reference-stable
branch and the main, the CI is not creating sync PR. This results in
growing gap between the stable reference and the main.

I've changed the CI behavior, so the PR is always created. The person
that is the author of last commit is assigned so they can fix potential
conflicts.

Author: Kordyjan

.github/workflows/language-reference.yaml

@@ -1,4 +1,4 @@
-name: language-reference-documentation
+name: Language reference documentation
 
 on:
   push:
@@ -14,14 +14,14 @@ permissions:
 
 jobs:
   build-and-push:
+    name: Build reference documentation and push it
     permissions:
       contents: write  # for Git to git push
-      pull-requests: write  # for peter-evans/create-pull-request to create a PR
     runs-on: ubuntu-latest
     steps:
       - name: Get current date
         id: date
-        run: echo "::set-output name=date::$(date +'%Y-%m-%d')"
+        run: echo "date=$(date +'%Y-%m-%d')" >> $GITHUB_OUTPUT
 
       - name: Git Checkout
         uses: actions/checkout@v3
@@ -67,26 +67,22 @@ jobs:
           fi
           cd ..
 
-      - name: Merge changes to main
-        if: github.event_name == 'push'
-        run: |
-          cd dotty
-          git fetch origin main:main
-          git checkout main
-          git config user.name gh-actions
-          git config user.email [email protected]
-          git merge language-reference-stable
-          cd ..
-
-      - name: Create pull request with backport to main
-        if: github.event_name == 'push'
-        uses: peter-evans/create-pull-request@v4
+  backport-to-main:
+    name: Create pull request with backport to main
+    permissions:
+      pull-requests: write  # for repo-sync/pull-request to create a PR
+    runs-on: ubuntu-latest
+    if: github.event_name == 'push' || github.event_name == 'workflow_dispatch'
+    steps:
+      - uses: actions/checkout@v3
+      - uses: repo-sync/pull-request@v2
         with:
-          path: dotty
-          branch: language-reference-backport
-          labels: area:documentation
-          title: Backport changes from stable documentation branch
-          body: This pull request is created automatically after push to stable documentation branch and backports the changes
-          reviewers: pikinier20,julienrf
-          assignees: pikinier20
+          destination_branch: main
+          pr_label: area:documentation
+          pr_title: Sync with the stable documentation branch
+          pr_body: |
+            This pull request is syncing the `main` with changes from `language-reference-stable`.
+
+            It was created automatically after ${{ github.event.head_commit.id }} by @${{ github.event.head_commit.author.username }}
+          pr_assignee: ${{ github.event.head_commit.author.username }}