fix(material/radio): required attribute being set on buttons

[naaajii]

fixes when MatRadioGroup is set to be required it was setting all of its MatRadioButton to be required as-well which is confusing for assistive technologies, this commit ensures we only set aria-required on group rather than all buttons unless button is being used standalone of MatRadioGroup

fixes #30399

[clamli]

Hi! Is there any update for this PR?

[naaajii]

ello @clamli! I think the PR has the necessary changes to fix the issue & its pending a review. however if you feel like anything is missing from it feel free to ping me.

[andrewseguin]

Hey sorry this dropped from our tasks @naaajii - can you rebase it and we can try to land it?