testsuite: fix flaky test in t0019-tbon-config.t #10127

Job	Run time
validate commits	9s
python linting	31s
spelling	5s
Generate build matrix	6s
bookworm - test-install	38s
bookworm - 32 bit	38s
noble - test-install	42s
el9 - test-install	39s
alpine - test-install	39s
fedora40 - test-install	35s
jammy - test-install	37s
focal - py3.8	37s
bookworm - gcc-12,content-s3,distcheck	38s
fedora40 - clang-18	37s
coverage	30s
el8 - ascii	36s
el8 - test-install	38s
el8 - system,coverage	36s
inception	37s
flux-accounting check	5s
flux-pmix check	1s
macos build only	1s
flux-pam check	1s
flux-sched check	1s
Generate docker manifest	1s
	10m 18s

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