Fix slack webhook trigger condition

[henryrecker-pingidentity]

Change Description

Align Slack webhook trigger with other repos, and do not trigger on manual workflow runs

Change Characteristics

• This PR contains beta functionality
• This PR requires introduction of breaking changes

Checklist

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• Check to confirm: I have performed a review of my PR against the PR checklist and confirm that:
  • Changes have proper unit and acceptance test coverage (including regression tests)
  • Impacted command, parameter and flag descriptions have been reviewed and updated
  • Impacted command examples have been reviewed and updated
  • Impacted documentation files have been reviewed and updated
  • Does not introduce breaking changes to commands, parameters or flags (unless required to do so)
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Required SDK Upgrades

Testing

This PR has been tested with:

• Unit tests (please paste commands and results below)
• Acceptance tests (please paste commands and results below)
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Testing Results

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