[ic-toggle-button-group] light disabled state isn't correct

[GCHQ-Developer-530]

Summary of the bug

When disabled is true and appearance is light, the text of the toggle buttons in a toggle button group is updated to disabled state, but the border around the toggle button group is still solid white.

I think it should be the disabled state border, or a lighter disabled state border with the dashed lines.

📸 Screenshots or code

🧐 Expected behaviour

Check with design, update border accordingly.

Also check dark appearance as well.

[MI6-255]

Dev to change border to a dashed grey border, in Figma

[mi6-577]

Figma shows dashed border for individual toggle buttons in disabled state, however toggle button group does not include a group state of disabled.

Design: Update figma to include missing state property on toggle button group

[mi6-577]

Changes made to v3 Figma and merged