CI: restore [allow_failure: true] for [publish_kernel_sdk]

What

CI: restore allow_failure: true for the job publish_kernel_sdk on master_branch pipelines.

Why

This value was accidentally(?) changed during the CIAO translation in !11501 (merged). Removing the allow_failure: true puts the whole pipeline in a pending state:

unless the job publish_kernel_sdk is executed. Additionally, this means that the pipeline never counts as "success" or "fail", and consequently we on longer get warning messages on slack when it fails.

How

CIAOing.

Manually testing the MR

Not sure. Merging it to prod?

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