test(gax-httpjson): add clean non-reflective unit tests for HttpJsonConscryptUtils and ManagedHttpJsonChannel

Author: lqiu96

sdk-platform-java/gax-java/gax-httpjson/src/test/java/com/google/api/gax/httpjson/ManagedHttpJsonChannelTest.java

@@ -39,7 +39,7 @@
 class ManagedHttpJsonChannelTest {
 
   @Test
-  void testBuilder_defaultHttpTransport_usesConscryptConfiguredTransport() {
+  void testBuilder_defaultHttpTransport_usesConscryptConfiguredTransport() throws Exception {
     ManagedHttpJsonChannel channel =
         ManagedHttpJsonChannel.newBuilder().setEndpoint("localhost:8080").build();
     assertThat(channel).isNotNull();