fix: Set persist-credentials to false in release-update-adk-web workflow

This resolves a "Duplicate header: Authorization" error (HTTP 400) when
create-pull-request runs. actions/checkout@v6 persists credentials by default,
which conflicts with the token used by create-pull-request.

Co-authored-by: Yifan Wang <wanyif@google.com>
PiperOrigin-RevId: 943548154

Author: wyf7107

.github/workflows/release-update-adk-web.yaml

@@ -38,7 +38,7 @@ jobs:
     - name: Checkout repository
       uses: actions/checkout@v6
       with:
-        token: ${{ secrets.RELEASE_PAT }}
+        persist-credentials: false
 
     - name: Fetch and unzip frontend assets
       run: |