add junit's category to image heap

Author: diegomarquezp

src/main/resources/META-INF/native-image/com.google.cloud/google-cloud-spanner-jdbc/native-image.properties

@@ -12,4 +12,5 @@ Args = --initialize-at-build-time==com.google.cloud.spanner.IntegrationTestEnv,\
   org.junit.runners.Parameterized,\
   org.junit.runner.RunWith,\
   org.junit.FixMethodOrder,\
+  org.junit.experimental.categories.Category,\
   java.lang.annotation.Annotation