Fix prod_whl_upload: use deploy key instead of github.token for cross-repo push to batfish/pybatfish

[Copilot]

github.token is scoped to the workflow's own repository (batfish/docker). Adding permissions: contents: write has no effect on pushes to batfish/pybatfish — those require a PAT.

Changes

• reusable-upload.yml: Declare PYBATFISH_GITHUB_TOKEN as a required secret input; use it for the actions/checkout of batfish/pybatfish (which also configures git credentials for the subsequent git push)
• cross_version_test.yml: Thread PYBATFISH_GITHUB_TOKEN: ${{ secrets.PYBATFISH_GITHUB_TOKEN }} through the secrets: blocks of both upload_dev and upload_prod callers

Required action

Create a repository secret PYBATFISH_GITHUB_TOKEN in batfish/docker → Settings → Secrets → Actions containing a PAT with Contents: write on batfish/pybatfish.

[batfish-bot]

This change is 

[dhalperi]

@dhalperi reviewed 2 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on copilot[bot]).