Update backport workflow to ignore changelog conflicts (opensearch-pr…

…oject#2729)

Signed-off-by: Miki <amoo_miki@yahoo.com>

Signed-off-by: Miki <amoo_miki@yahoo.com>
Signed-off-by: Arpit Bandejiya <abandeji@amazon.com>

.github/workflows/backport.yml

@@ -22,10 +22,9 @@ jobs:
           # opensearch-trigger-bot installation ID
           installation_id: 22958780
 
-      # Using fork of https://github.com/tibdex/backport
-      # https://github.com/tibdex/backport/pull/81
       - name: Backport
-        uses: VachaShah/backport@v1.1.4
+        uses: VachaShah/backport@v2.1.0
         with:
           github_token: ${{ steps.github_app_token.outputs.token }}
           branch_name: backport/backport-${{ github.event.number }}
+          files_to_skip: "CHANGELOG.md"