[9.1] Replace -1s with -1 in ML forecast tests (#134016)#134040

elasticsearchmachine merged 1 commit intoelastic:9.1elastic/elasticsearch:9.1from

JeremyDahlgren:backport/9.1/pr-134016JeremyDahlgren/elasticsearch:backport/9.1/pr-134016Copy head branch name to clipboard