fix: set correct http.route to root span

[DmytryS]

Which problem is this PR solving?

• When nested express routers used, wrong http.route set in root span (api prefix used instead). The real route can be deep inside of child spans, when request matches route and appropriate handler used.

Short description of the changes

• When nested routers are used, and response made from end handler, response goes up through all routers that causes set api prefix for root router at the end
• That also make sense because route length can't become less anyway

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