Small improvement in new_developers.md #18031

Job	Run time
doctest (1.10, Linux, RPTU, normal-memory)	22m 56s
doctest (1.11, Linux, RPTU, normal-memory)	22m 0s
doctest (nightly, Linux, RPTU, normal-memory)	24m 59s
doctest (1.10, Linux, RPTU, normal-memory, depwarn=error)	24m 8s
test (1.6, short, Linux)	19m 8s
doctest (1.10, macOS, RPTU)	16m 22s
test (1.6, long, Linux)	17m 49s
test (1.10, short, Linux)	18m 36s
test (1.10, long, Linux)	18m 20s
test (1.11, short, Linux)	17m 24s
test (1.11, long, Linux)	14m 15s
test (nightly, short, Linux)	2h 30m 17s
test (nightly, long, Linux)	17m 45s
test (1.10, short, Linux, RPTU, high-memory, depwarn=error)	17m 28s
test (1.10, long, Linux, RPTU, normal-memory, depwarn=error)	16m 33s
test (1.10, short, macOS, RPTU)	13m 19s
test (1.10, long, macOS, RPTU)	13m 7s
test (1.10, book, Linux, RPTU, normal-memory)	38m 40s
test (nightly, book, Linux, RPTU, normal-memory)	2h 30m 16s
	10h 33m 22s

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