Do not enforce using a hash with hidden ci key

Merged Grzegorz Bizon requested to merge fix/ci-config-hidden-key-validation into master

What does this MR do?

This MR remove the validation rule that was to strict.

Why was this MR needed?

Enforcing hidden CI job configuration to be a hash, narrows options of using YAML anchors, and was not backwards compatbile.

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #21512 (closed)