Escape Slack notification inputs

[GabrielBianconi]

Fix #3718

First PR with Sonnet 4.5

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Important

Escapes inputs for Slack notifications in GitHub workflow to prevent injection attacks.

• Behavior:
  • Escapes inputs for Slack notifications in .github/workflows/slack-notifications.yml using jq to build payloads for various GitHub events.
  • Handles events: issues, issue_comment, pull_request_target, pull_request_review, discussion, and discussion_comment.
• Implementation:
  • Adds separate steps to build payloads for each event type, ensuring inputs are properly escaped.
  • Updates Slack notification steps to use pre-built payloads from previous steps.

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[Copilot]

Pull Request Overview

This PR escapes Slack notification inputs to prevent potential security issues and JSON injection vulnerabilities in GitHub Actions workflow notifications. The change refactors inline payload definitions to use proper JSON construction with jq for safe input handling.

• Extracts JSON payload construction into dedicated build steps using jq for proper escaping
• Replaces inline YAML payload definitions with references to safely constructed payloads
• Applies consistent escaping pattern across all notification types (issues, comments, PRs, discussions)

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