test : added unit tests for KeyboardShortcutsModal component - #3

Summary of What Has Been Done

Created components/KeyboardShortcutsModal.test.tsx with comprehensive unit tests covering:

• No rendering when isOpen is false
• Correct rendering when isOpen is true (dialog, heading, shortcut groups)
• Closes on backdrop click
• Closes on X (close) button click
• Closes on Escape key press
• Body scroll is locked when open and restored when closed
• Navigation and General shortcut groups render correctly
• Kbd elements render for shortcut keys
• Footer hint renders with the ? toggle instruction

Changes Made

• New file: components/KeyboardShortcutsModal.test.tsx

Impact it Made

Adds first unit test coverage for the KeyboardShortcutsModal component, ensuring correct open/close behavior and accessibility features work correctly.

Closes #8418.

Note: please assign this PR to the tmdeveloper007 account.