minor symfony#61550 [Console] Add phpdoc for return type of subscribed signals (nesl247)

This PR was squashed before being merged into the 7.4 branch.

Discussion
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[Console] Add phpdoc for return type of subscribed signals

| Q             | A
| ------------- | ---
| Branch?       | 7.4
| Bug fix?      | yes
| New feature?  | no <!-- if yes, also update src/**/CHANGELOG.md -->
| Deprecations? | no <!-- if yes, also update UPGRADE-*.md and src/**/CHANGELOG.md -->
| Issues        |
| License       | MIT

The signals are integers, but the array return type was missing. This meant we had to add this to every implementation to prevent phpstan from complaining.

Commits
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8885fc4 [Console] Add phpdoc for return type of subscribed signals

Author: nicolas-grekas

src/Symfony/Component/Console/Command/SignalableCommandInterface.php

@@ -20,6 +20,10 @@ interface SignalableCommandInterface
 {
     /**
      * Returns the list of signals to subscribe.
+     *
+     * @return list<\SIG*>
+     *
+     * @see https://php.net/pcntl.constants for signals
      */
     public function getSubscribedSignals(): array;