[sidebar] fix #371 - reduced line-height of expand/collapse btn header icon

[mattgoud]

❓ Types of changes

fix #371 - reduced line-height of expand/collapse btn header icon

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• 📦 New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

📝 Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes
• The component exists on old Prestashop UIKit and my pull request on migrating documentation is accepted.