[ENH] concatenate runs at first level #634

Job	Run time
tests (system, moae, ubuntu-latest, R2022b)	28m 21s
tests (system, moae, macos-latest, R2022b)	1h 14m 26s
tests (system, facerep, ubuntu-latest, R2022b)	45m 37s
tests (system, facerep, macos-latest, R2022b)	52m 10s
tests (system, fmriprep, ubuntu-latest, R2022b)	8m 36s
tests (system, fmriprep, macos-latest, R2022b)	15m 55s
tests (system, ubuntu-latest, R2022b, bms)	28m 1s
tests (unit, ubuntu-latest, R2022b, fast)	15m 14s
tests (unit, macos-latest, R2022b, fast)	26m 17s
tests (unit, ubuntu-latest, R2022b, slow)	17m 45s
tests (unit, macos-latest, R2022b, slow)	36m 54s
	5h 49m 16s

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