minor #40768 [HttpClient] [PHPDoc] Fix 2 remaining return mixed (fancyweb)

This PR was merged into the 4.4 branch.

Discussion
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[HttpClient] [PHPDoc] Fix 2 remaining return mixed

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Two cases I forgot in https://github.com/symfony/symfony/pull/40728 😕

Commits
-------

97a43e1dab [HttpClient][PHPDoc] Fix 2 remaining return mixed

src/Symfony/Component/HttpClient/Response/HttplugPromise.php

@@ -49,10 +49,8 @@ final class HttplugPromise implements HttplugPromiseInterface
 
     /**
      * {@inheritdoc}
-     *
-     * @return Psr7ResponseInterface|mixed
      */
-    public function wait($unwrap = true)
+    public function wait($unwrap = true): ?Psr7ResponseInterface
     {
         $result = $this->promise->wait($unwrap);
 

src/Symfony/Contracts/HttpClient/ResponseInterface.php

@@ -104,8 +104,8 @@ interface ResponseInterface
      *
      * Other info SHOULD be named after curl_getinfo()'s associative return value.
      *
-     * @return array|mixed An array of all available info, or one of them when $type is
-     *                     provided, or null when an unsupported type is requested
+     * @return mixed An array of all available info, or one of them when $type is
+     *               provided, or null when an unsupported type is requested
      */
     public function getInfo(string $type = null);
 }