GH-5744: migrate rdf4j-sail-memory to Jackson 3

Update QueryPlanRetrievalTest to use
tools.jackson.databind.{JsonNode,ObjectMapper} instead of
com.fasterxml.jackson.databind. Jackson 3 arrives transitively, so no
pom.xml change is required.

Author: aschwarte10

core/sail/memory/src/test/java/org/eclipse/rdf4j/sail/memory/QueryPlanRetrievalTest.java

@@ -49,8 +49,8 @@
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
-import com.fasterxml.jackson.databind.JsonNode;
-import com.fasterxml.jackson.databind.ObjectMapper;
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.ObjectMapper;
 
 public class QueryPlanRetrievalTest {