run all commands silently

To avoid leaking any potentially sensitive information, all commands are now run
without logging to the console. Logging can be enabled by turning on debug logging
as described at https://docs.github.com/en/actions/how-tos/monitor-workflows/enable-debug-logging.

Updates tailscale/corp#33405

Signed-off-by: Percy Wegmann <percy@tailscale.com>