Add automatic issue closure to Check for Copilot Model Updates workflow

[Copilot]

The workflow creates issues when models are missing but never closes them when resolved. This creates stale issues that require manual cleanup.

Changes

Added automatic issue closure

• New workflow step runs when needs_update=false
• Finds open issues with title "🤖 Action Required: Update Copilot Supported Models" and label maintenance
• Posts closing comment and closes issue automatically

Added workflow triggers for model data files

• Triggers on push to src/tokenEstimators.json and src/modelPricing.json
• Enables immediate validation when developers fix missing models
• Creates feedback loop: issue creation → developer fixes → automatic verification → issue closure

Workflow behavior

# Before: Only create path
Missing models → Create issue → [Manual closure required]

# After: Complete lifecycle
Missing models → Create issue → Models added → Workflow runs → Close issue

Original prompt

Update the workflow "Check for Copilot Model Updates" to close any open issue when there are no open models to be added to the list.

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.