Fix failing test for SOLR-16962; update log must be enabled (#2537)

diff --git a/solr/core/src/test/org/apache/solr/update/CustomTLogDirTest.java b/solr/core/src/test/org/apache/solr/update/CustomTLogDirTest.java
index 5ca9a2d..3c284e8 100644
--- a/solr/core/src/test/org/apache/solr/update/CustomTLogDirTest.java
+++ b/solr/core/src/test/org/apache/solr/update/CustomTLogDirTest.java
@@ -78,6 +78,7 @@
     Path ulogDir = Path.of("../");
 
     Path configSet = LuceneTestCase.createTempDir();
+    System.setProperty("enable.update.log", "true");
     System.setProperty("solr.test.sys.prop2", "proptwo");
     System.setProperty("solr.ulog.dir", ulogDir.toString()); // picked up from `solrconfig.xml`
     SolrTestCaseJ4.copyMinConf(configSet.toFile(), null, "solrconfig.xml");