cmux-next: the popup address field draws no focus ring
Every webviews job on feat-cmux-next is red at check:text-focus. fa8b3fcdda (Chrome-style popup windows) made the popup URL label selectable, so a click gives it the keyboard and AppKit draws a focus ring. The guard asks for focusRingType = .none on any selectable label (scripts/cmux-next/check-text-focus-rings.py).
This adds that one line to PopupLocationBarView.swift.
Seen on #21623 and #21954 (CI / web / react-apps-check), both of which fail only on this.
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Summary by cubic
Fixes the popup location bar drawing a focus ring when its URL label is selected.
PopupLocationBarView.swift now sets focusRingType = .none on the address field, so clicking the selectable URL doesn't display an AppKit focus ring, satisfying the check:text-focus guard on all feat-cmux-next webviews jobs.