Matrix builds may fail updating badges

[Mulugruntz]

See this job: https://github.com/Mulugruntz/celery-pubsub/actions/runs/4167158182/jobs/7212395387#step:5:258

To https://github.com/Mulugruntz/celery-pubsub.git
 ! [remote rejected] HEAD -> shields (cannot lock ref 'refs/heads/shields': is at 0564340ab257b3da2019922adf94804da00ef1a7 but expected 4daa6ffb078a9a62aa23ca21a6babff2e9f0f4f1)
error: failed to push some refs to '***github.com/Mulugruntz/celery-pubsub.git'

This is because I have a bunch of jobs in a matrix and by the time a job starts then end, another one may have also ended and pushed in the meantime.
This is quite a sneaky one, and could easily be missed.

Moreover, as it shows on the next line:

Docker Action run completed with exit code 0

it might be complicated to detect and restart (not that it would be a super clean solution...).