test: remove wildcard in test class import (#3634)

Author: zhumin8

gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/GrpcTransportChannelTest.java

@@ -30,7 +30,7 @@
 
 package com.google.api.gax.grpc;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 
 import io.grpc.ManagedChannel;
 import org.junit.jupiter.api.Test;