improve scalability of `flux overlay errors` #10185

Job	Run time
Generate build matrix	11s
Generate build matrix	11s
validate commits	9s
validate commits	9s
python linting	31s
python linting	31s
spelling	8s
spelling	8s
bookworm - test-install	12m 7s
bookworm - test-install	12m 7s
bookworm - 32 bit	13m 18s
bookworm - 32 bit	13m 18s
noble - test-install	13m 30s
noble - test-install	13m 30s
el9 - test-install	12m 23s
el9 - test-install	12m 23s
alpine - test-install	12m 27s
alpine - test-install	12m 27s
fedora40 - test-install	12m 17s
fedora40 - test-install	12m 17s
jammy - test-install	11m 54s
jammy - test-install	11m 54s
focal - py3.8	16m 49s
focal - py3.8	16m 49s
bookworm - gcc-12,content-s3,distcheck	19m 58s
bookworm - gcc-12,content-s3,distcheck	19m 58s
fedora40 - clang-18	3m 0s
fedora40 - clang-18	16m 48s
coverage	24m 3s
coverage	24m 3s
el8 - ascii	19m 30s
el8 - ascii	19m 30s
el8 - test-install	13m 46s
el8 - test-install	13m 46s
el8 - system,coverage	7m 23s
el8 - system,coverage	7m 23s
inception	21m 25s
inception	21m 25s
flux-accounting check	4m 45s
flux-accounting check	4m 45s
flux-pmix check	13m 19s
flux-pmix check	13m 19s
flux-sched check	6m 39s
flux-sched check	6m 39s
flux-pam check	4m 15s
flux-pam check	4m 15s
macos build only	3m 18s
macos build only	3m 18s
Generate docker manifest	0s
Generate docker manifest	1s
	8h 27m 59s

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