Default to running the scenario tests on an arm iOS simulator variant on an Apple Silicon host Mac (#39210)

* Default to using an arm iOS simulator variant on Apple Silicon

* Kick tests

testing/scenario_app/run_ios_tests.sh

diff --git a/testing/scenario_app/run_ios_tests.sh b/testing/scenario_app/run_ios_tests.sh
index 74b32a0..bd0a6f8 100755
--- a/testing/scenario_app/run_ios_tests.sh
+++ b/testing/scenario_app/run_ios_tests.sh
@@ -27,7 +27,11 @@
 SCRIPT_DIR=$(follow_links "$(dirname -- "${BASH_SOURCE[0]}")")
 SRC_DIR="$(cd "$SCRIPT_DIR/../../.."; pwd -P)"
 
-FLUTTER_ENGINE="ios_debug_sim_unopt"
+if uname -m | grep "arm64"; then
+  FLUTTER_ENGINE="ios_debug_sim_unopt_arm64"
+else
+  FLUTTER_ENGINE="ios_debug_sim_unopt"
+fi
 
 if [[ $# -eq 1 ]]; then
   FLUTTER_ENGINE="$1"