Ensure accessibility shortcut preference summaries are not focusable

In this case, keyboard focusability causes TalkBack to exclude summary
text from the grouped content surfaced when focusing the top-level list
item.

Bug: 400538324
Test: Manually with TalkBack, including ClickableSpan in summaries
Flag: EXEMPT bug fix
Change-Id: Ib8bc3276aee857121381de7bc4e23e05cd512383