workflows/check: don't check github api for owners file

This removes the "owners" check from codeowners-validator. With it, all
tokens and permissions can be removed, because these were only needed to
make these requests.

This solves the problem of codeowners-validator not supporting our new
nested team structure for nixpkgs-maintainers. To make the onboarding of
new teams easier, we moved all teams "under" the nixpkgs-maintainers
team. This makes them inherit the right privileges (triage) for Nixpkgs.

However, this inheritance is not recognized by codeowners-validator,
thus it assumes that these teams don't have access to Nixpkgs. This then
fails the owners check immediately.

Removing the owners check also has a few other advantages:
- This check depends on external state: If a user is renamed or a team
removed, the check will fail. This makes it a bad check for required
status checks or merge queues - the check might fail randomly,
independent of the current PR.
- Running this check in a fork will never work, because the respective
users and teams don't have access to the fork's repo.

Both of this required us to set `continue-on-error: true` most of the
time.

ci/github-script/prepare.js

@@ -221,7 +221,6 @@ module.exports = async ({ github, context, core, dry }) => {
 
     const touched = []
     if (files.includes('ci/pinned.json')) touched.push('pinned')
-    if (files.includes('ci/OWNERS')) touched.push('owners')
     core.setOutput('touched', touched)
 
     return