Updates all workflow files and actionlint config to use ubuntu-latest
instead of the deprecated runners-privilegedescalation self-hosted runner.
Co-Authored-By: Paperclip <noreply@paperclip.ing>
ARC runner scale set was recreated on 2026-03-19 with label
`runners-privilegedescalation` but all shared workflows still referenced
`local-ubuntu-latest`. This label mismatch caused startup_failure on
every Release workflow and queued CI jobs with no runner to pick them up.
Updates all 4 workflows and the actionlint config to match the current
ARC runner scale set label.
Closes#27