HSEARCH-4155 Add a missing "static" keyword

Signed-off-by: Yoann Rodière <yoann@hibernate.org>

util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/rule/BackendMock.java

@@ -300,7 +300,7 @@ public SchemaManagementWorkCallListContext work(StubSchemaManagementWork.Type ty
 		}
 	}
 
-	public class DocumentWorkCallListContext {
+	public static class DocumentWorkCallListContext {
 		private final String indexName;
 		private final String tenantId;
 		private final DocumentCommitStrategy commitStrategyForDocumentWorks;