t0009-dmesg.t: `not ok 18 - dmesg -H, --human works`

[grondo]

t0009-dmesg.t failed in a bookworm,distcheck builder during CI on master.
I don't think we've seen this error before. I'm not sure why these tests are failing,

2026-02-09T22:26:11.5235092Z expecting success: 
2026-02-09T22:26:11.5235272Z 	#
2026-02-09T22:26:11.5235520Z 	#  Note: --human option should format first timestamp of dmesg output
2026-02-09T22:26:11.5235929Z 	#   as [MmmDD HH:MM] and second line should be an offset thereof
2026-02-09T22:26:11.5236295Z 	#   e.g. [  +0.NNNNNN]. The following regexes attempt to verify
2026-02-09T22:26:11.5236611Z 	#   that --human produced this pattern.
2026-02-09T22:26:11.5237029Z 	#
2026-02-09T22:26:11.5237199Z 	flux dmesg --human | sed -n 1p \
2026-02-09T22:26:11.5237482Z 	    | grep "^\[[A-Z][a-z][a-z][0-3][0-9] [0-9][0-9]:[0-9][0-9]\]" &&
2026-02-09T22:26:11.5237777Z 	flux dmesg --human | sed -n 2p \
2026-02-09T22:26:11.5238000Z 	    | grep "^\[ *+[0-9]*\.[0-9]*\]"
2026-02-09T22:26:11.5238149Z 
2026-02-09T22:26:11.5238248Z [Feb09 22:13] logger.notice[0]: hello_wrap2
2026-02-09T22:26:11.5238505Z not ok 18 - dmesg -H, --human works
2026-02-09T22:26:11.5238667Z 
2026-02-09T22:26:11.5238742Z expecting success: 
2026-02-09T22:26:11.5238952Z 	flux dmesg --human --delta | sed -n 1p \
2026-02-09T22:26:11.5239244Z 	    | grep "^\[[A-Z][a-z][a-z][0-3][0-9] [0-9][0-9]:[0-9][0-9]\]" &&
2026-02-09T22:26:11.5239546Z 	flux dmesg --human --delta | sed -n 2p \
2026-02-09T22:26:11.5239901Z 	    | grep "^\[ *+[0-9]*\.[0-9]*\]"
2026-02-09T22:26:11.5240061Z 
2026-02-09T22:26:11.5240151Z [Feb09 22:13] logger.notice[0]: hello_wrap2
2026-02-09T22:26:11.5240419Z not ok 19 - dmesg -H, --human --delta works

I can't think of why this test would fail off the top of my head. May have to add debugging to get more information next time.