is-*: fix for bash v3, for macos cron #435

Job	Run time
fresh-macos-test	11m 22s
login-shells-and-linting	6m 7s
distro-test (ubuntu:latest)	3m 51s
homebrew-macos-test	10m 15s
distro-test (fedora:latest)	5m 13s
distro-test (debian:latest)	3m 56s
distro-test (alpine:latest)	7m 26s
distro-test (manjarolinux/base)	3m 50s
distro-test (opensuse/leap)	7m 44s
distro-test (opensuse/tumbleweed)	4m 17s
distro-test (kalilinux/kali-rolling)	3m 58s
	1h 7m 59s

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