fix: deactivate stale in-progress deployments before creating new ones

[0x46616c6b]

Type of Change

• Bugfix
• Enhancement / new feature
• Refactoring
• Documentation

Description

When the Kustomization is updated in quick succession (e.g. two pushes to main within seconds), GitHub Deployments can become orphaned — stuck in in_progress forever. This happens because the deploy.staffbase.com/deployment-id annotation in the GitOps repo gets overwritten by the subsequent run, and the flux-deployment-reporter only sees the latest ID.

This adds a deactivate_stale_deployments() function that runs before each new deployment creation. It queries existing deployments for the target environment via the GitHub API and marks any with status in_progress, queued, or pending as inactive ("Superseded by newer deployment").

The cleanup is best-effort (failures don't block new deployments) and idempotent (concurrent runs deactivating the same deployment is harmless).

Note: GitHub's built-in auto_inactive parameter only affects deployments that previously reached success state and does not help with orphaned in_progress deployments.

Checklist

• Write tests
• Make sure all tests pass
• Update documentation
• Review the Contributing Guideline and sign CLA
• Reference relevant issue(s) and close them after merging

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_{The changes and the PR were generated by Claude.}