prevent erroneous route interception during lazy fetch (#64692)
When the router cache can't find a cache node for the requested segment,
it performs a request to the server to get the missing data. This
request to the server currently will always include the `next-url`
header, and on soft-navigations, the router will route the request to
the intercepted handler. This lazy fetch is treated as a soft navigation
by the server, and will incorrectly return data for the intercepted
route.
Similar to the handling in `router.refresh`, and the server action
reducer, we should not include the `next-url` header if there's no
interception route currently in the tree, as otherwise we'll be
erroneously triggering the intercepted route.
Fixes #64676
Closes NEXT-3146
