minor #20074 fix dump destination value in PHP config (xabbuh)

This PR was merged into the 6.4 branch.

Discussion
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fix dump destination value in PHP config

Let the value be the same to what we configure with the YAML and XML examples.

Commits
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c6c0908 fix dump destination value in PHP config

Author: xabbuh

reference/configuration/debug.rst

@@ -99,7 +99,7 @@ Typically, you would set this to ``php://stderr``:
 
         return static function (ContainerConfigurator $container): void {
             $container->extension('debug', [
-                'dump_destination' => 'tcp://%env(VAR_DUMPER_SERVER)%',
+                'dump_destination' => 'php://stderr',
             ]);
         };