minor symfony#49414 Fix Request locale property doc types (bytestream)

This PR was submitted for the 6.2 branch but it was merged into the 5.4 branch instead.

Discussion
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Fix Request locale property doc types

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |
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As shown by https://github.com/symfony/symfony/blob/b9eef0fb17a75b533b67ae15d291126a1ae8c93f/src/Symfony/Component/HttpFoundation/Request.php#L1391 the `locale` property can be `null`.

Commits
-------

a05604e Fix Request locale property doc types

Author: nicolas-grekas

src/Symfony/Component/HttpFoundation/Request.php

@@ -191,7 +191,7 @@ class Request
     protected $session;
 
     /**
-     * @var string
+     * @var string|null
      */
     protected $locale;
 
@@ -1452,7 +1452,7 @@ public function setLocale(string $locale)
      */
     public function getLocale()
     {
-        return null === $this->locale ? $this->defaultLocale : $this->locale;
+        return $this->locale ?? $this->defaultLocale;
     }
 
     /**