Update build promotion workflow so it doesn't send an error AND a no candidate message.

[rbarker-dev]

Problem Statement

Currently if no build candidate is found to be promoted we send the message that there was no candidate found, then we also send an alert for failure. As seen here.

Proposed Solution

We need to update the Report Build Promotion Failure step to include the condition ${{ needs.determine-build-candidate.outputs.promote-build-candidate == 'false' }}.

This allows us to cleanly report to the build promotion channel once and only once.

Business Need

This is required to avoid cluttering the slack channels that are reported to.