Update terminology once whatwg/html#8463 is fixed

[sbingler]

https://github.com/httpwg/http-extensions/pull/2480 updated 6265bis with new HTML terminology, but "target browsing context" wasn't yet changed. whatwg/html#8463 is tracking that work and once it is fixed then 6265bis can use the updated term.

See https://github.com/httpwg/http-extensions/pull/2480#discussion_r1150041961 https://github.com/httpwg/http-extensions/pull/2480#discussion_r1157844049

This is low priority work and may be deferred if needed.