codecov uploads in github actions failing with nonsense error message

[grahamgower]

Failing codecov upload error:

error - 2026-03-29 06:27:23,460 -- Upload queued for processing failed: {"message":"Token required because branch is protected"}
==> Failed to run upload-coverage
    Exiting...
Error: Process completed with exit code 1.

From: https://github.com/popsim-consortium/demes-python/actions/runs/23687904960/job/69050561796#step:7:359

This is total crap, because

1. we're using a token, and
2. we don't have any branch protection rules (unless dependabot branches are funny somehow?)