prefer std::is_sorted to ranges::is_sorted to avoid issues with missing operator ==
Fixes debug assert check build failures, as seen in
https://lhcb-nightlies.cern.ch/nightly/lhcb-lcg-dev3/build/1023/
Issue appears to be ranges::is_sorted
(incorrectly) needs operator ==
to be defined.
Edited by Marco Cattaneo