Workaround occasional failures of docker system prune in public runne…

…rs (#38825)

Occasionally `docker syetem prune` fails on Public docker runners with

file resize error: truncate /var/lib/docker/buildkit/containerdmeta.db:
read-only file system

This happens after docker has been already cleaned and should have no
side efects if the metadata db could not be truncated.

Ignoring error in this case should allow the job to continue.

scripts/ci/cleanup_docker.sh

@@ -16,7 +16,7 @@
 # specific language governing permissions and limitations
 # under the License.
 function cleanup_docker {
-    docker system prune --all --force --volumes
+    docker system prune --all --force --volumes || true
 }
 
 cleanup_docker