The test workflows checkout the private rustfs/auto-testing repository, but
the default GITHUB_TOKEN only has access to rustfs/rustfs, so every checkout
failed with 'repository ... not found' (nightly runs on 2026-08-28).
Pass secrets.PF_TESTING_GH_TOKEN (the existing cross-repo PAT already used
by the performance workflow) to the auto-testing checkout steps in all three
workflows.