Fix Namespace Assignment Test (#10289)

When a namespace is declared without a "=" assignment, there should be an error. I think the test did not check that the ouput contains an error. Noticed this because I saw an extra stack trace when running a test.

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Author: jesswrd

script/tool/test/gradle_check_command_test.dart

@@ -710,16 +710,19 @@ dependencies {
         pluginName: pluginName, includeNameSpaceAsDeclaration: false);
     writeFakeManifest(example, isApp: true);
 
+    Error? commandError;
     final List<String> output = await runCapturingPrint(
         runner, <String>['gradle-check'], errorHandler: (Error e) {
-      print((e as ToolExit).stackTrace);
+      commandError = e;
     });
 
+    expect(commandError, isA<ToolExit>());
     expect(
         output,
         containsAllInOrder(
           <Matcher>[
-            contains('Validating android/app/build.gradle'),
+            contains('build.gradle must set a "namespace"'),
+            contains('The following packages had errors:'),
           ],
         ));
   });