Add command_prefix to parallel_bench #123

Job	Run time
Build/Test ubuntu-latest clang fastbuild	45m 26s
Build/Test arm-ubuntu-arm-22.04-16core clang fastbuild	8m 42s
Build/Test arm-ubuntu-arm-22.04-16core gcc fastbuild	8m 46s
Build/Test ubuntu-latest clang opt	1h 12m 27s
Build/Test ubuntu-latest gcc opt	44m 9s
Build/Test arm-ubuntu-arm-22.04-16core gcc opt	8m 56s
Build/Test ubuntu-latest gcc fastbuild	28m 49s
Build/Test arm-ubuntu-arm-22.04-16core clang opt	9m 36s
	3h 46m 51s

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