The signal icons were recently updated and are now implemented as CSS custom properties in signal-icons.scss.
We need to replace the old icons with the new ones across all components.

✅ What to do

• Update the signal icons used in form validation (refer to the form creation guideline).
• Update the icons used in toasts.
• Check for other components using signal icons and update them accordingly (all design occurrences are listed in [Signal icons] Redesign warning and error icon #6360).