[ARM Auto SignOff] Incorrectly removing label `ARMSignedOff`, if trivial=true

PR:
- https://github.com/Azure/azure-rest-api-specs/pull/39353

Workflow run with bug:
- https://github.com/Azure/azure-rest-api-specs/actions/runs/21654131664/job/62425266643

wf starts, PR has label ARMSignedOff:

you determine, auto-signoff yes, due to trivial-changes:

L93: auto-signoff=yes
L33: you flip ARMSignedOff from true to false

From: Akhila
> Ah, I know why. Thats because the trivial change auto sign off is enabled in test mode, so we dont want to add the ARMAutoSignOff label, hence set to false.