fix graalVM tests

Author: rahul2393

java-spanner/google-cloud-spanner/src/test/resources/META-INF/native-image/com.google.cloud/google-cloud-spanner/native-image.properties

@@ -1,3 +1,4 @@
 Args=--initialize-at-build-time=org.junit.runner.RunWith \
  --initialize-at-build-time=org.junit.experimental.categories.Category \
- --initialize-at-build-time=org.junit.runners.model.FrameworkField
+ --initialize-at-build-time=org.junit.runners.model.FrameworkField \
+ -H:DynamicProxyConfigurationResources=${.}/proxy-config.json

java-spanner/google-cloud-spanner/src/test/resources/META-INF/native-image/com.google.cloud/google-cloud-spanner/proxy-config.json

@@ -0,0 +1,5 @@
+[
+  {
+    "interfaces": ["org.mockito.plugins.MockMaker"]
+  }
+]