Address Net::SSH::HostKeyMismatch seen locally between bin/test runs.

test/integration/docker/deployer/setup.sh

@@ -21,3 +21,7 @@ install_kamal
 push_image_to_registry_4443 nginx 1-alpine-slim
 push_image_to_registry_4443 traefik v2.9
 push_image_to_registry_4443 busybox 1.36.0
+
+# .ssh is on a shared volume that persists between runs. Clean it up as the
+# churn of temporary vm IPs can eventually create conflicts.
+rm -f /root/.ssh/known_hosts