Skip scheduled runs when the workflow already ran on the same commit #205

Nightly and other scheduled workflows that validate code (integration specs, nightly builds, benchmarks and similar) rerun even when nothing has changed since they last ran on the same head commit. Provide a shared way for a scheduled run to check whether the same workflow already completed successfully for the current commit and, if so, skip its jobs. Roll it out to the scheduled code-validation workflows across Cratis repositories.

Health and monitoring workflows that check live systems rather than code (for example chronicle-health and sign-in-health) are out of scope; they must keep running on schedule.

Status

State: Done
Scope: Shared scheduled-code validation guard and agreed code-only rollout. Health/monitoring schedules and schedules depending on outside inputs are excluded.
Delivered: Shared action: https://github.com/Cratis/Workflows/tree/main/.github/actions/skip-if-already-ran. Other repository rollout was reported complete in #205 (comment); the remaining Studio adoption is completed in Cratis/StudioIssues#906 and uses the guard to gate specs in https://github.com/Cratis/Studio/blob/main/.github/workflows/integration-specs.yml.
Remaining: Nothing for the agreed code-only rollout.
Follow-ups: None.