Add CI workflow for renovate configuration validation

[JAORMX]

Summary

Adds a CI workflow to automatically validate the renovate configuration whenever changes are made to renovate.json or the workflow itself.

Changes

• New workflow: .github/workflows/renovate-config-validation.yml
• JSON validation: Verifies renovate.json is valid JSON with proper schema
• Configuration validation: Uses renovate-config-validator to catch configuration errors
• Smart triggers: Runs on changes to renovate.json or the workflow file itself

Benefits

• ✅ Early feedback: Catches renovate configuration errors before they affect the bot
• ✅ Automated validation: No manual validation needed when updating renovate config
• ✅ Maintainable: Avoids hard-coding patterns that could get out of sync
• ✅ Comprehensive: Validates both JSON syntax and renovate-specific configuration

Workflow Triggers

• Pull requests that modify renovate.json or the workflow file
• Pushes to main branch that modify these files
• Manual dispatch for testing
• Can be called by other workflows

Validation Steps

1. JSON syntax check: Ensures renovate.json is valid JSON
2. Schema validation: Verifies the renovate schema is defined
3. Configuration validation: Runs renovate-config-validator to catch configuration errors

This workflow will help maintain the quality of our renovate configuration and provide immediate feedback when issues are introduced.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.01%. Comparing base (30b658b) to head (8e63478).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1946      +/-   ##
==========================================
- Coverage   47.02%   47.01%   -0.02%     
==========================================
  Files         223      223              
  Lines       27669    27669              
==========================================
- Hits        13011    13008       -3     
- Misses      13660    13662       +2     
- Partials      998      999       +1     

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