minor #21028 [Console] Updated phpdoc on return types (mlpo)

This PR was merged into the 2.7 branch.

Discussion
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[Console] Updated phpdoc on return types

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

The return type of “ask” is not necessarily a string (notice that “doAsk” may return mixed type).
Same for “validateAttempts” (validator may return something else than a string).

Commits
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442a304292 [Console] Updated phpdoc on return types

src/Symfony/Component/Console/Helper/QuestionHelper.php

@@ -37,7 +37,7 @@ class QuestionHelper extends Helper
      * @param OutputInterface $output   An OutputInterface instance
      * @param Question        $question The question to ask
      *
-     * @return string The user answer
+     * @return mixed The user answer
      *
      * @throws \RuntimeException If there is no data to read in the input stream
      */
@@ -383,7 +383,7 @@ class QuestionHelper extends Helper
      * @param OutputInterface $output      An Output instance
      * @param Question        $question    A Question instance
      *
-     * @return string The validated response
+     * @return mixed The validated response
      *
      * @throws \Exception In case the max number of attempts has been reached and no valid response has been given
      */