Lowercase GitHub Actions label and status

This is visually easier, as uppercased labels turn into camelcase when
appearing in a row of badges.

It is also consistent with existing practice on shields.io, and the
manual badge examples presently on the osh website.
0 jobs for !2 with lowercase
latest yaml invalid error detached

Found errors in your .gitlab-ci.yml:

  • Project `OCamlPro/gitlab-deployments` not found or access denied!
You can also test your .gitlab-ci.yml in CI Lint