json_elements: stream_range_as_array, stream_object: mark lambda mutable
json_elements: stream_range_as_array, stream_object: mark lambda mutable

Otherwise the captured objects will get copied when
moved later when lambda is called.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/seastar,avikivity/seastar,scylladb/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,avikivity/seastar,avikivity/seastar,syuu1228/seastar