Rephrase null safety mode (#74306)

packages/flutter_tools/lib/src/commands/build.dart

@@ -67,7 +67,7 @@ abstract class BuildSubCommand extends FlutterCommand {
       globals.printStatus('💪 Building with sound null safety 💪', emphasis: true);
     } else {
       globals.printStatus(
-        'Building with unsound null safety',
+        'Building without sound null safety',
         emphasis: true,
       );
       globals.printStatus(

packages/flutter_tools/test/general.shard/commands/build_test.dart

@@ -67,7 +67,7 @@ void main() {
     );
 
     FakeBuildSubCommand().test(unsound);
-    expect(testLogger.statusText, contains('Building with unsound null safety'));
+    expect(testLogger.statusText, contains('Building without sound null safety'));
 
     testLogger.clear();
     FakeBuildSubCommand().test(sound);