minor #48793 Leverage arrow function syntax for closure (tigitz)

This PR was merged into the 6.3 branch.

Discussion
----------

Leverage arrow function syntax for closure

| Q             | A
| ------------- | ---
| Branch?       | 6.3
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | Fix #47658 <!-- prefix each issue number with "Fix #", no need to create an issue if none exists, explain below instead -->
| License       | MIT
| Doc PR        | <!-- required for new features -->

Rationale in the RFC [here](https://wiki.php.net/rfc/arrow_functions_v2#introduction)

It's also notable that using arrow function syntax rather than the classic one has been enforced in the past by symfony core member: symfony/symfony#48069 (comment)

So this PR would be consistent.

Commits
-------

f5802d3a2a Leverage arrow function syntax for closure

DependencyInjection/RegisterListenersPass.php

@@ -83,7 +83,7 @@ public function process(ContainerBuilder $container)
                     $event['method'] = 'on'.preg_replace_callback([
                         '/(?<=\b|_)[a-z]/i',
                         '/[^a-z0-9]/i',
-                    ], function ($matches) { return strtoupper($matches[0]); }, $event['event']);
+                    ], fn ($matches) => strtoupper($matches[0]), $event['event']);
                     $event['method'] = preg_replace('/[^a-z0-9]/i', '', $event['method']);
 
                     if (null !== ($class = $container->getDefinition($id)->getClass()) && ($r = $container->getReflectionClass($class, false)) && !$r->hasMethod($event['method']) && $r->hasMethod('__invoke')) {

Tests/EventDispatcherTest.php

@@ -347,7 +347,7 @@ public function testDispatchLazyListener()
     public function testRemoveFindsLazyListeners()
     {
         $test = new TestWithDispatcher();
-        $factory = function () use ($test) { return $test; };
+        $factory = fn () => $test;
 
         $this->dispatcher->addListener('foo', [$factory, 'foo']);
         $this->assertTrue($this->dispatcher->hasListeners('foo'));
@@ -363,7 +363,7 @@ public function testRemoveFindsLazyListeners()
     public function testPriorityFindsLazyListeners()
     {
         $test = new TestWithDispatcher();
-        $factory = function () use ($test) { return $test; };
+        $factory = fn () => $test;
 
         $this->dispatcher->addListener('foo', [$factory, 'foo'], 3);
         $this->assertSame(3, $this->dispatcher->getListenerPriority('foo', [$test, 'foo']));
@@ -376,7 +376,7 @@ public function testPriorityFindsLazyListeners()
     public function testGetLazyListeners()
     {
         $test = new TestWithDispatcher();
-        $factory = function () use ($test) { return $test; };
+        $factory = fn () => $test;
 
         $this->dispatcher->addListener('foo', [$factory, 'foo'], 3);
         $this->assertSame([[$test, 'foo']], $this->dispatcher->getListeners('foo'));

Tests/ImmutableEventDispatcherTest.php

@@ -75,7 +75,7 @@ public function testHasListenersDelegates()
     public function testAddListenerDisallowed()
     {
         $this->expectException(\BadMethodCallException::class);
-        $this->dispatcher->addListener('event', function () { return 'foo'; });
+        $this->dispatcher->addListener('event', fn () => 'foo');
     }
 
     public function testAddSubscriberDisallowed()
@@ -89,7 +89,7 @@ public function testAddSubscriberDisallowed()
     public function testRemoveListenerDisallowed()
     {
         $this->expectException(\BadMethodCallException::class);
-        $this->dispatcher->removeListener('event', function () { return 'foo'; });
+        $this->dispatcher->removeListener('event', fn () => 'foo');
     }
 
     public function testRemoveSubscriberDisallowed()