shell: ignore SIGPIPE #9973

Job	Run time
validate commits	9s
Generate build matrix	6s
python linting	28s
spelling	8s
bookworm - test-install	12m 32s
bookworm - 32 bit	13m 37s
noble - test-install	12m 37s
el9 - test-install	12m 2s
alpine - test-install	12m 27s
fedora40 - test-install	11m 51s
jammy - test-install	11m 49s
focal - py3.8	16m 47s
bookworm - gcc-12,content-s3,distcheck	19m 53s
fedora40 - clang-18	17m 5s
coverage	24m 28s
el8 - ascii	19m 47s
el8 - test-install	13m 5s
el8 - system,coverage	7m 30s
inception	21m 49s
flux-pam check	4m 7s
flux-pmix check	13m 16s
flux-sched check	7m 2s
flux-accounting check	4m 45s
Generate docker manifest	1s
	4h 17m 21s

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