Fix name confusion between SuperInExtensionTest and SuperInExtensionTypeTest

Previously, both super_in_extension_test.dart and
super_in_extension_type_test.dart contained a class called
SuperInExtensionTest. Rename the one in
super_in_extension_type_test.dart to avoid confusion.

Change-Id: Ic55c91a02245baf2c31adcf68122198ffb87653e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/363706
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/analyzer/test/src/diagnostics/super_in_extension_type_test.dart

@@ -9,12 +9,12 @@ import '../dart/resolution/context_collection_resolution.dart';
 
 main() {
   defineReflectiveSuite(() {
-    defineReflectiveTests(SuperInExtensionTest);
+    defineReflectiveTests(SuperInExtensionTypeTest);
   });
 }
 
 @reflectiveTest
-class SuperInExtensionTest extends PubPackageResolutionTest {
+class SuperInExtensionTypeTest extends PubPackageResolutionTest {
   test_binaryOperator() async {
     await assertErrorsInCode('''
 extension type A(int it) {