Enable a couple of tests that were disabled because they

tests/standalone/io/regress_6521_test.dart

Index: tests/standalone/io/regress_6521_test.dart
diff --git a/tests/standalone/io/regress-6521.dart b/tests/standalone/io/regress_6521_test.dart
similarity index 96%
rename from tests/standalone/io/regress-6521.dart
rename to tests/standalone/io/regress_6521_test.dart
index a02025d2cb74ad103b4f4440d687cc7b66adf021..9d393b703d01c62e1c4a4e625d2100173e8af9d6 100644
--- a/tests/standalone/io/regress-6521.dart
+++ b/tests/standalone/io/regress_6521_test.dart
@@ -18,10 +18,6 @@ void main() {
       req.inputStream.read();
       rsp.outputStream.close();
     };
-    req.inputStream.onClosed = () {
-      client.shutdown();
-      server.close();
-    };
   };
 
   var connection = client.openUrl(
@@ -36,6 +32,8 @@ void main() {
     response.inputStream.onClosed = () {
       // Wait with closing the client request until the response is done.
       clientRequest.outputStream.close();
+      client.shutdown();
+      server.close();
     };
   };
 }