Update the permissions for validate-description

[saisravani20]

Summary

This PR improves the PR description validation workflow to fix failures in private repositories and provides clearer error messages. The main fix adds explicit permissions (pull-requests: read, contents: read) to ensure GITHUB_TOKEN can access PR data in all repository types.

Related Issues

• work-item: https://app.devrev.ai/devrev/works/ISS-231700

Type of Change

• Change doesn't affect products or customers
• Bug fix (non-breaking change which fixes an issue)
• Non-breaking change (the new functionality and code refactor do not require a migration strategy)
• Breaking change (fix or feature that will require a migration plan for data or other services)
• Documentation/comment update
• Other (please describe):

Testing Procedure

Checklist

• I used generative AI to generate this PR
• I have self-reviewed my code for clarity and correctness
• I have added or updated comments for complex or non-obvious logic in my code
• I have updated relevant documentation (e.g., README, code docs)
• My changes do not introduce new warnings or errors
• I have added or updated tests to cover new or changed functionality
• All tests pass locally with my changes applied

[devrev-jo]

LG with comment

[devrev-jo]

LG