Bugfix for missing return type TreeBuilder from ConfigurationInterface in Symfony 7

[mkilmanas]

Fixes this incompatibility with Symfony 7 (or symfony/config:^7.0 to be precise):

PHP Fatal error:  Declaration of Prooph\Bundle\EventStore\DependencyInjection\Configuration::getConfigTreeBuilder() must be compatible with Symfony\Component\Config\Definition\ConfigurationInterface::getConfigTreeBuilder(): Symfony\Component\Config\Definition\Builder\TreeBuilder in /.../vendor/prooph/event-store-symfony-bundle/src/DependencyInjection/Configuration.php on line 29

P.S. For whatever reason running composer install in this bundle's repository, even with --no-dev still refuses to install symfony/config v7.0+ - so the issue is not immediately obvious, but it popped up in an actual project.
Heres symfony interface now: https://github.com/symfony/symfony/blob/7.0/src/Symfony/Component/Config/Definition/ConfigurationInterface.php

[mkilmanas]

@unixslayer any chance you could have a look at this, and make a patch release if possible?

[coveralls]

Pull Request Test Coverage Report for Build 9227591538

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.939%

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Totals
Change from base Build 9179036425:	0.0%
Covered Lines:	527
Relevant Lines:	561

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💛 - Coveralls