Lots of composer deprecation warnings about PSR-4 compliance

[itsjavi]

I am getting a lot of warnings when installing/updating the package, saying something like: Class (name) does not comply with psr-4 autoloading standard. It will not autoload anymore in Composer v2.0.

Example of affected classes:

• Matthias\SymfonyDependencyInjectionTest\Tests\PhpUnit\DependencyInjection\DefinitionHasTagConstraintTest
• Matthias\SymfonyConfigTest\Tests\PartialConfigurationIntegrationTest

As you can see it also affects your other SymfonyConfigTest package.

[rolfdenhartog]

I've created a PR for this: #132

[Nyholm]

Thank you. The PR is merged.