Fix tool exit message shown when user provides a non-list to "assets" for a deferred component (#137837)

Fixes #136163

Author: andrewkolos

packages/flutter_tools/lib/src/flutter_manifest.dart

@@ -642,7 +642,7 @@ void _validateDeferredComponents(MapEntry<Object?, Object?> kvp, List<String> er
       if (valueMap.containsKey('assets')) {
         final Object? assets = valueMap['assets'];
         if (assets is! YamlList) {
-          errors.add('Expected "assets" key in the $i element of "${kvp.key}" to be a list, but got $assets (${assets.runtimeType}).');
+          errors.add('Expected "assets" to be a list, but got $assets (${assets.runtimeType}).');
         } else {
           _validateListType<String>(assets, errors, '"assets" key in the $i element of "${kvp.key}"', 'file paths');
         }

packages/flutter_tools/test/general.shard/flutter_manifest_test.dart

@@ -1459,7 +1459,7 @@ flutter:
     );
 
     expect(flutterManifest, null);
-    expect(logger.errorText, 'Expected "assets" key in the 0 element of "deferred-components" to be a list, but got blah (String).\n');
+    expect(logger.errorText, 'Expected "assets" to be a list, but got blah (String).\n');
   });
 
   testWithoutContext('FlutterManifest parses asset-only deferred components', () async {