minor #33705 Fix return type of Process::restart() (derrabus)

This PR was merged into the 3.4 branch.

Discussion
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Fix return type of Process::restart()

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | N/A
| License       | MIT
| Doc PR        | N/A

`Process::restart()` is annotated with `@return $this`, but it actually returns a clone of the current object. So `@return static` would be more appropriate.

Commits
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7d7380d9e7 Fix return type of Process::restart().

src/Symfony/Component/Process/Process.php

@@ -363,7 +363,7 @@ class Process implements \IteratorAggregate
      * @param callable|null $callback A PHP callback to run whenever there is some
      *                                output available on STDOUT or STDERR
      *
-     * @return $this
+     * @return static
      *
      * @throws RuntimeException When process can't be launched
      * @throws RuntimeException When process is already running