[fix](test) fix unstable lower case test (apache#46410)

### What problem does this PR solve?

when "use_meta_cache" = "false", the meta sync between FEs maybe delay,
and it may cause the case unstable, so I added a `wait()` method to wait
the meta sync.

regression-test/suites/external_table_p0/lower_case/test_lower_case_meta_show_and_select.groovy

@@ -15,6 +15,10 @@
 // specific language governing permissions and limitations
 // under the License.
 
+import java.util.concurrent.Executors
+import java.util.concurrent.TimeUnit
+import org.awaitility.Awaitility
+
 suite("test_lower_case_meta_show_and_select", "p0,external,doris,external_docker,external_docker_doris") {
 
     String jdbcUrl = context.config.jdbcUrl
@@ -24,6 +28,18 @@ suite("test_lower_case_meta_show_and_select", "p0,external,doris,external_docker
     String bucket = getS3BucketName()
     String driver_url = "https://${bucket}.${s3_endpoint}/regression/jdbc_driver/mysql-connector-j-8.3.0.jar"
 
+    def wait_table_sync = { String db ->
+        Awaitility.await().atMost(10, TimeUnit.SECONDS).pollInterval(1, TimeUnit.SECONDS).until{
+            try {
+                def res = sql "show tables from ${db}"
+                return res.size() > 0;
+            } catch (Exception e) {
+                e.printStackTrace();
+                return false;
+            }
+        }
+    }
+
     try_sql """drop user ${jdbcUser}"""
     sql """create user ${jdbcUser} identified by '${jdbcPassword}'"""
     sql """grant all on *.*.* to ${jdbcUser}"""
@@ -75,6 +91,7 @@ suite("test_lower_case_meta_show_and_select", "p0,external,doris,external_docker
             "include_database_list" = "external_test_lower,external_test_UPPER"
         )"""
 
+    wait_table_sync("test_cache_false_lower_false.external_test_lower")
     test {
         sql """show databases from test_cache_false_lower_false"""
 
@@ -172,6 +189,7 @@ suite("test_lower_case_meta_show_and_select", "p0,external,doris,external_docker
             "include_database_list" = "external_test_lower,external_test_UPPER"
         )"""
 
+    wait_table_sync("test_cache_false_lower_true.external_test_lower")
     test {
         sql """show databases from test_cache_false_lower_true"""