Fix duplicate Authorization header causing process-submission workflow failure

[Copilot]

peter-evans/create-pull-request@v6 was failing with remote: Duplicate header: "Authorization" (HTTP 400) because actions/checkout@v7 persists credentials into the local git config, and create-pull-request then injects its own Authorization header on top — resulting in two headers on the same request.

Change

• Added persist-credentials: false to actions/checkout@v7 so git config is left clean, letting create-pull-request own authentication exclusively via its token input.

- name: Checkout repository
  uses: actions/checkout@v7
  with:
    persist-credentials: false