[ic-radio-group] toggling disabled state doesn't work

[GCHQ-Developer-530]

Summary of the bug

When toggling disabled between true and false on the radio group, it doesn't change anything visually. Behind the scenes it sets the input label to disabled but the styling isn't actually coming through.

I tried adding a watch on disabled to update it to a new value, and also to add removeDisabledFalse but this had no affect either.

🪜 How to reproduce

Tell us the steps to reproduce the problem:

1. Go to playground example (will be done after 1970)
2. Set disabled to true
3. See the error

📸 Screenshots or code

🧐 Expected behaviour

I would expect that it would pass down to the child radios to show their disabled state and also show a disabled state for the group label.

[MI6-255]

Add a test for setting disabled on the group