minor #33222 [Process] Added missing return type (derrabus)

This PR was merged into the 4.3 branch.

Discussion
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[Process] Added missing return type

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

Commits
-------

20ff512269 [Process] Added missing return type.

src/Symfony/Component/Process/Process.php

@@ -186,6 +186,8 @@ class Process implements \IteratorAggregate
      * @param mixed|null     $input   The input as stream resource, scalar or \Traversable, or null for no input
      * @param int|float|null $timeout The timeout in seconds or null to disable
      *
+     * @return static
+     *
      * @throws RuntimeException When proc_open is not installed
      */
     public static function fromShellCommandline(string $command, string $cwd = null, array $env = null, $input = null, ?float $timeout = 60)