Enable unit testing gRPC retries in CI

Author: chusitoo

ci/do_ci.sh

@@ -360,6 +360,7 @@ elif [[ "$1" == "cmake.exporter.otprotocol.test" ]]; then
         -DWITH_OTLP_HTTP=ON \
         -DWITH_OTLP_FILE=ON \
         -DWITH_OTLP_GRPC_SSL_MTLS_PREVIEW=ON \
+        -DWITH_OTLP_RETRY_PREVIEW=ON \
         "${SRC_DIR}"
   grpc_cpp_plugin=`which grpc_cpp_plugin`
   proto_make_file="CMakeFiles/opentelemetry_proto.dir/build.make"