docker: make script portable for macOS #67

Job	Run time
spelling	7s
Generate build matrix	7s
validate commits	0s
python linting	30s
bookworm	10m 16s
bookworm - 32 bit	10m 16s
bookworm - gcc-12,content-s3,distcheck	10m 17s
bookworm - py3.11,clang-15	10m 15s
coverage	10m 16s
jammy - test-install	10m 7s
bookworm - test-install	10m 16s
focal - py3.8	10m 14s
el8	10m 14s
el8 - ascii	10m 14s
el8 - system,coverage	6m 4s
fedora34 - gcc-11.2,py3.9	10m 14s
fedora38 - gcc-13.1,py3.11	10m 15s
fedora39 - gcc-13.2,py3.12	10m 13s
alpine	10m 17s
inception	10m 16s
flux-accounting check	4m 39s
flux-pam check	4m 3s
flux-pmix check	9m 51s
flux-sched check	6m 39s
Generate docker manifest	1s
	3h 5m 41s

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