Fix PR update flow and allow updates from release branches (#3780)

Signed-off-by: Sambhav Kothari <skothari44@bloomberg.net>

.github/workflows/pr-update.yaml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - 'main'
+      - 'release-*'
 jobs:
   autoupdate:
     permissions:
@@ -13,8 +14,8 @@ jobs:
       - name: Automatically update PR
         uses: adRise/update-pr-branch@437fab6e0ac7d2a668f2c479f64225edd7f303fd # v0.6.0
         with:
-          token: ${{ secrets.GITHUB_TOKEN }}
+          token: ${{ secrets.PR_UPDATE_TOKEN }}
-          base: 'main'
+          base: ${{ env.GITHUB_REF_NAME }}
           required_approval_count: 1
           require_passed_checks: true
           sort: 'updated'