buildscripts: checkout matching grpc/grpc branch for xds test (#6828)
buildscripts: checkout matching grpc/grpc branch for xds test (#6828)


grpc/grpc-java,grpc/grpc-java,stanley-cheung/grpc-java,ejona86/grpc-java,dapengzhang0/grpc-java,dapengzhang0/grpc-java,dapengzhang0/grpc-java,grpc/grpc-java,stanley-cheung/grpc-java,grpc/grpc-java,stanley-cheung/grpc-java,dapengzhang0/grpc-java,ejona86/grpc-java,stanley-cheung/grpc-java,ejona86/grpc-java,ejona86/grpc-java