Fix run_with_poller.sh to pass shellcheck
diff --git a/test/core/util/run_with_poller.sh b/test/core/util/run_with_poller.sh
index 0579145..382a63e 100755
--- a/test/core/util/run_with_poller.sh
+++ b/test/core/util/run_with_poller.sh
@@ -16,4 +16,4 @@
 set -ex
 export GRPC_POLL_STRATEGY=$1
 shift
-$@
+"$@"