Update symfony/event-dispatcher requirement from ^4.0 to ^5.1

[dependabot-preview]

Updates the requirements on symfony/event-dispatcher to permit the latest version.

Release notes

Sourced from symfony/event-dispatcher's releases.

v5.1.3

Changelog (symfony/event-dispatcher@v5.1.2...v5.1.3)

• bug #37341 Fix support for PHP8 union types (nicolas-grekas)

Changelog

Sourced from symfony/event-dispatcher's changelog.

CHANGELOG

5.1.0

• The LegacyEventDispatcherProxy class has been deprecated.
• Added an optional dispatcher attribute to the listener and subscriber tags in RegisterListenerPass.

5.0.0

• The signature of the EventDispatcherInterface::dispatch() method has been changed to dispatch($event, string $eventName = null): object.
• The Event class has been removed in favor of Symfony\Contracts\EventDispatcher\Event.
• The TraceableEventDispatcherInterface has been removed.
• The WrappedListener class is now final.

4.4.0

• AddEventAliasesPass has been added, allowing applications and bundles to extend the event alias mapping used by RegisterListenersPass.
• Made the event attribute of the kernel.event_listener tag optional for FQCN events.

4.3.0

• The signature of the EventDispatcherInterface::dispatch() method should be updated to dispatch($event, string $eventName = null), not doing so is deprecated
• deprecated the Event class, use Symfony\Contracts\EventDispatcher\Event instead

4.1.0

• added support for invokable event listeners tagged with kernel.event_listener by default
• The TraceableEventDispatcher::getOrphanedEvents() method has been added.
• The TraceableEventDispatcherInterface has been deprecated.

4.0.0

• removed the ContainerAwareEventDispatcher class
• added the reset() method to the TraceableEventDispatcherInterface

3.4.0

• Implementing TraceableEventDispatcherInterface without the reset() method has been deprecated.

3.3.0

Commits

• 7827d55 Merge branch '5.0' into 5.1
• 5c5dd86 Merge branch '4.4' into 5.0
• 6140fc7 Fix support for PHP8 union types
• cc0d059 Merge branch '5.0' into 5.1
• 9f2efcb Merge branch '4.4' into 5.0
• a5370aa Use ">=" for the "php" requirement
• 203100f Merge branch '5.0'
• d5d80b8 Merge branch '4.4' into 5.0
• dccd982 Fix register event listeners compiler pass
• c90d70a Merge branch '5.0'
• Additional commits viewable in compare view

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[dependabot-preview]

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[juliusknorr]

Nope, we need to be somewhat aligned with the sever release here (see #1965)

[dependabot-preview]

OK, I won't notify you again about this release, but will get in touch when a new version is available.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.