minor #23565 [DI] Mark Container::$privates as internal (nicolas-grekas)

This PR was merged into the 3.2 branch.

Discussion
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[DI] Mark Container::$privates as internal

| Q             | A
| ------------- | ---
| Branch?       | 3.2
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

As is should have been since its introduction.

Commits
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2725fd6080 [DI] Mark Container::$privates as internal

src/Symfony/Component/DependencyInjection/Container.php

@@ -56,10 +56,14 @@ class Container implements ResettableContainerInterface
 
     protected $services = array();
     protected $methodMap = array();
-    protected $privates = array();
     protected $aliases = array();
     protected $loading = array();
 
+    /**
+     * @internal
+     */
+    protected $privates = array();
+
     private $underscoreMap = array('_' => '', '.' => '_', '\\' => '_');
     private $envCache = array();