fix: fix the issue triage assignment wflow

[GangGreenTemperTatum]

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Proposed changes

• Enable workflow triggers for issue events
• Fix token handling by moving to github-script's 'with' section
• Add proper assignee deduplication and validation
• Filter out 'TBC' placeholder assignees
• Implement graceful error handling for invalid assignees
• Add informative logging and issue comments for failures
• Remove workflow failures on non-critical errors
• Clean up duplicate GITHUB_TOKEN declaration

The workflow now properly handles edge cases and provides better feedback
when assignments fail, without interrupting the automation process.

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have x-referenced the appropriate issue this addresses within the projects board
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