CI: revert !20210 (scripts: add auth for sccache on protected branches)

What

• Reverts !20210 (merged). (NB: had previously been reverted and reapplied).

Why

oc.build_kernels is failing which prevents the documentation to be updated.

How

• Revert the reapply of !20210 (merged).
• Quick fix to unblock the doc update. Not a long term solution:
  • We should fix sccache auth on gcs for protected branches. !20210 (merged) works but not on all Docker images.
  • Doc update pipeline probably does not need oc.build_kernels (cf. #8170)

Manually testing the MR

Look at this test documentation.update pipeline: https://gitlab.com/tezos/tezos/-/pipelines/2223974396

• all jobs are green even documentation:publish (but no doc update is done).
• NB: it runs on a protected branch.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR

Closes #8174 (closed)