Replace use of project owner in disabled worker notifier

What does this MR do and why?

We're moving towards Owner role being possible in Projects. Because multiple owners will be possible soon, we are phasing out owner.

This replaces a usage of project.owner in the code.

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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Related to #350603 (closed)