chore(spanner-jdbc): disable flaky AppTest.testRunApplication (#14858)

Disable flaky
`com.google.cloud.jdbc.quickperf.AppTest.testRunApplication`.

b/579436547

Author: jinseopkim0

java-spanner-jdbc/samples/quickperf/src/test/java/com/google/cloud/jdbc/quickperf/AppTest.java

@@ -39,6 +39,7 @@
 import javax.annotation.Nonnull;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.springframework.boot.SpringApplication;
 import org.testcontainers.containers.GenericContainer;
@@ -144,6 +145,7 @@ private static Connection createConnection() throws SQLException {
     return DriverManager.getConnection(url, properties);
   }
 
+  @Ignore("Flaky test: b/579436547")
   @Test
   public void testRunApplication() throws Exception {