EventSplit test streams write to seperate files Fixes ATEAM-682
This is a follow up to !38671 (closed) and !38655 (merged)
Correct the AthenaPoolMultiTest_AthenaPoolMultiTestEventSplit_ctest to have each of the split streams write to a separate file. The "Bad" stream was sharing an output file with the "Others" stream, probably by accident.
Rationale: setting multiple streams to write to the same file causes problems. Should the streams' metadata item lists overlap the shared items will add more entries to the metadata tree than the others causing a failure when attempting to close the file after writing. If the two lists are the same the resulting metadata tree has multiple entries, which may lead to undefined behavior.
There is no reason to expect multiple output streams to need to write to the same file. We do not support that configuration, and should not test for it.
Bonus (?): adds some lines that seem to have appeared from a change to the TrkTrackSummaryUpdater