Fix flaky connection count in mysqli test

Use connection ID instead of count to check whether we're using a
persistent connection. This allows the test to be run in parallel with
the other tests, but also protects against the possibility that some
other service connects to the mysql server.

Closes GH-18040

Author: iluuu1994

ext/mysqli/tests/bug73462.phpt

@@ -5,21 +5,14 @@ mysqli
 --SKIPIF--
 <?php
 require_once('skipifconnectfailure.inc');
-/*
- * TODO: this test is flaky with persistent connections on PPC CI runner
- * [001] Expected '8711' got '8712'.
- */
-if (gethostname() == "php-ci-ppc64be") {
-    die("SKIP test is flaky");
-}
 ?>
 --FILE--
 <?php
     require_once("connect.inc");
 
     /* Initial persistent connection */
     $mysql_1 = new mysqli('p:'.$host, $user, $passwd, $db, $port);
-    $result = $mysql_1->query("SHOW STATUS LIKE 'Connections'");
+    $result = $mysql_1->query("SELECT CONNECTION_ID()");
     $c1 = $result->fetch_row();
     $result->free();
     $mysql_1->close();
@@ -35,7 +28,7 @@ if (gethostname() == "php-ci-ppc64be") {
     /* Re-use persistent connection */
     $mysql_3 = new mysqli('p:'.$host, $user, $passwd, $db, $port);
     $error = mysqli_connect_errno();
-    $result = $mysql_3->query("SHOW STATUS LIKE 'Connections'");
+    $result = $mysql_3->query("SELECT CONNECTION_ID()");
     $c3 = $result->fetch_row();
     $result->free();
     $mysql_3->close();