It took me too long to find this. 😓

If you need to delete all workflow runs of a GitHub Action, you can do it with PowerShell using this GitHub cli command:

gh run list --limit 1000 --json databaseId -q '.[].databaseId' | ForEach-Object { gh run delete $_ }

Or this Bash / Git Bash GitHub cli command:

gh run list --limit 1000 --json databaseId -q '.[].databaseId' | xargs -I{} gh run delete {}