allen_single_track_tos test failing (race condition)

the allen_single_track_tos test is failing, probably because of a race condition with another test (both trying to write to the same file)

Error in <TFile::TFile>: file /workspace/build/Moore/build/Hlt/Hlt1Conf/qmtest_tmp/allen_monitor.root already exists

/cc @lhcb-rta-maintainers