Ensure test failures are reported on the flutter customer test registry. (#8581)

tool/flutter_customer_tests/test.sh

diff --git a/tool/flutter_customer_tests/test.sh b/tool/flutter_customer_tests/test.sh
index 340bb02..713f670 100755
--- a/tool/flutter_customer_tests/test.sh
+++ b/tool/flutter_customer_tests/test.sh
@@ -6,6 +6,9 @@
 # setup.sh, which is called from the setup steps in
 # https://github.com/flutter/tests/blob/main/registry/flutter_devtools.test.
 
+# Ensure test failures are reported.
+set -e
+
 # Test all tests in devtools_app_shared
 cd packages/devtools_app_shared
 flutter pub get