Concurrency Tests - Update ExternalBatch for symfony/proces v4.1+

Before
------

`api_v3_JobProcessMailingTest::testConcurrency()` and `Civi\FlexMailer\ConcurrencyTest`
fail when executed on Drupal 10.

After
-----

Pass when executed on Drupal 10

Technical Details
-----------------

`symfony/process` v4.1 deprecated the usage of `new Process(string)` and
added `Process::fromShellCommandline(string)`. The `new Process(string)` was
dropped from v5.x and v6.x. So you get an unconditional failure on D10. (On
other platforms, it can also fail... depending on how you deal with
deprecations.)

In `civicrm-core:composer.json`, the minimum mversion of `symfony/process` is `4.4`.
So that means we can use the newer `Process::fromShellCommandline(string)`.

Civi/API/ExternalBatch.php

@@ -217,7 +217,7 @@ public function createProcess($apiCall) {
     $env = array_merge($this->env, [
       'CIVICRM_SETTINGS' => $this->settingsPath,
     ]);
-    return new Process($command, $this->root, $env);
+    return Process::fromShellCommandline($command, $this->root, $env);
   }
 
   /**