Register composer-based set in PHPUnitSetProvider

[TomasVotruba]

withComposerBased(phpunit: true) resolves SetGroup::PHPUNIT through PHPUnitSetProvider, which only lists the per-version upgrade sets. The new composer-based.php set was not among them, so it was only reachable by naming PHPUnitSetList::COMPOSER_BASED explicitly, or indirectly through phpunit110.php and newer.

It is registered now, for any installed PHPUnit version:

// applies to any installed PHPUnit version, the rules and configuration inside are bound
// to the exact version they are available from
new ComposerTriggeredSet(
    SetGroup::PHPUNIT,
    'phpunit/phpunit',
    '>=4.0',
    __DIR__ . '/../../../config/sets/composer-based.php'
),

The set does its own gating - every rule in it declares a ComposerPackageConstraint, and the configuration goes through ruleWithConfigurationComposerVersionBound() - so loading it on any version is safe; nothing inside applies below the version it belongs to.

Verified against this package (PHPUnit ^13.2 installed):

$setManager->matchBySetGroups([SetGroup::PHPUNIT]);

phpunit130.php
composer-based.php

Requires rectorphp/rector-src#8245, which allows a version constraint instead of only a bare major version in ComposerTriggeredSet. composer.json points at that branch so CI can run; to be reverted to dev-main once it is merged.