t2812-flux-job-last.t sporadic hangs in CI

[grondo]

I've seen this one occur a couple times in CI. t2812-flux-job-last.t gets stuck in CI here:

  ok 7 - flux job last N lists the last N jobs
  flux job last N lists the last N jobs

 expecting success: 
  	flux job last "[:]" >lastdump.exp &&
  	flux dump dump.tgz &&
  	flux start -o,-Scontent.restore=dump.tgz \
  		flux job last "[:]" >lastdump.out &&
  	test_cmp lastdump.exp lastdump.out
  
  
  flux-dump: archived 1 keys
  flux-dump: archived 2 keys
  flux-dump: archived 3 keys
  flux-dump: archived 4 keys
  flux-dump: archived 5 keys
  flux-dump: archived 6 keys
  flux-dump: archived 7 keys
  flux-dump: archived 8 keys
  flux-dump: archived 9 keys
  flux-dump: archived 57 keys
  Mar 21 17:35:35.080540 job-manager.err[0]: replay warning: INACTIVE action failed on job fHYCzL7: Read-only file system
  Mar 21 17:35:35.399411 job-manager.err[0]: sched.alloc-response: id=fHZgycT already allocated