Set ApproxEventsPerBasket to 1 for FSRs (backport !3871)
This doesn't quite fix the tests (eg https://lhcb-nightlies.web.cern.ch/nightly/lhcb-run2-patches/1232/LHCb/x86_64_v2-centos7-gcc11-opt/tests#FSRAlgs) - they are still fractionally above the failure threshold - but it helps
Edited by Mark Smith