adjust timing tests (#758) #91

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	29m 38s
ci (a6osx, macos-12)	15m 54s
ci (ta6osx, macos-12)	19m 52s
ci (i3le, ubuntu-22.04)	12m 40s
ci (ti3le, ubuntu-22.04)	15m 53s
ci (a6le, ubuntu-22.04)	9m 2s
ci (ta6le, ubuntu-22.04)	12m 6s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 38s
ci (i3nt, windows-2022, vs)	11m 55s
ci (ti3nt, windows-2022, vs)	14m 58s
ci (a6nt, windows-2022, vs)	13m 22s
ci (ta6nt, windows-2022, vs)	15m 42s
ci (ta6nt, windows-2022, gcc)	12m 46s
	3h 12m 26s

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