fix port-bol? return type #56

Job	Run time
ci (tpb, ubuntu-22.04, --pb --threads --enable-libffi, test-some-fast)	30m 28s
ci (a6osx, macos-12)	19m 50s
ci (ta6osx, macos-12)	23m 13s
ci (i3le, ubuntu-22.04)	16m 34s
ci (ti3le, ubuntu-22.04)	16m 29s
ci (a6le, ubuntu-22.04)	10m 7s
ci (ta6le, ubuntu-22.04)	18m 36s
ci (ta6le, ubuntu-22.04, reboot, -m=ta6le --force, re.boot SCHEME="chezscheme", test-some-fast)	8m 40s
ci (i3nt, windows-2022, vs)	12m 14s
ci (ti3nt, windows-2022, vs)	15m 36s
ci (a6nt, windows-2022, vs)	13m 1s
ci (ta6nt, windows-2022, vs)	22m 29s
ci (ta6nt, windows-2022, gcc)	19m 40s
	3h 46m 57s

Provide feedback