Update pub to use the VM's new bad-snapshot exit code.

sdk/lib/_internal/pub/test/cache/repair/updates_binstubs_test.dart

Index: sdk/lib/_internal/pub/test/cache/repair/updates_binstubs_test.dart
diff --git a/sdk/lib/_internal/pub/test/cache/repair/updates_binstubs_test.dart b/sdk/lib/_internal/pub/test/cache/repair/updates_binstubs_test.dart
index 1d612a1b6162a8d6523aa8b8bc274dab54b246ea..e84f4e8cd16c7e48823c0653713bbf01f8afe057 100644
--- a/sdk/lib/_internal/pub/test/cache/repair/updates_binstubs_test.dart
+++ b/sdk/lib/_internal/pub/test/cache/repair/updates_binstubs_test.dart
@@ -57,8 +57,8 @@ main() {
     // The broken versions should have been replaced.
     d.dir(cachePath, [
       d.dir('bin', [
-        // 255 is the VM's exit code upon seeing an out-of-date snapshot.
-        d.matcherFile(binStubName('foo-script'), contains('255'))
+        // 253 is the VM's exit code upon seeing an out-of-date snapshot.
+        d.matcherFile(binStubName('foo-script'), contains('253'))
       ])
     ]).validate();
   });