[CI] update backport custom branch name (#2766) (#2784)

GitHub action for backporting got updated to change custom branch
to head template.

This was causing issues in clean up and skipping steps.

Issue:
n/a

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>

Signed-off-by: Kawika Avilla <kavilla414@gmail.com>
(cherry picked from commit bfe6b6b)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

.github/workflows/backport.yml

@@ -37,5 +37,5 @@ jobs:
         uses: VachaShah/backport@v2.1.0
         with:
           github_token: ${{ steps.github_app_token.outputs.token }}
-          branch_name: backport/backport-${{ github.event.number }}
+          head_template: backport/backport-<%= number %>-to-<%= base %>
           files_to_skip: "CHANGELOG.md"