[UT] Fix testConcurrentlyDropDbAndCreateTable running too slow (#43470)

Signed-off-by: Dejun Xia <[email protected]>
(cherry picked from commit 5b42b0e)

fe/fe-core/src/test/java/com/starrocks/server/ConcurrentDDLTest.java

@@ -150,7 +150,7 @@ public void testConcurrentlyDropDbAndCreateTable() throws Exception {
             Thread controlThread = new Thread(() -> {
                 int times = 0;
                 Random random = new Random();
-                while (times < 10) {
+                while (times < 5) {
                     try {
                         System.out.println("creating table and db time: " + times);
                         starRocksAssert.withDatabase("concurrent_test_db");