deps: update dependency com.google.errorprone:error_prone_core to v2.20.0 (#1115)

Author: renovate-bot

pom.xml

@@ -143,7 +143,7 @@
     <github.global.server>github</github.global.server>
     <site.installationModule>google-cloud-datastore-parent</site.installationModule>
     <project.javadoc.protobufBaseURL>https://googleapis.dev/java/google-api-grpc/latest</project.javadoc.protobufBaseURL>
-    <error-prone.version>2.19.1</error-prone.version>
+    <error-prone.version>2.20.0</error-prone.version>
   </properties>
 
   <dependencyManagement>