Issue #3574741: Fix loss of deprecated class extension detection with PHPStan 2.x

Gábor Hojtsyrequested to merge
issue/upgrade_status-3574741:3574741-4.x-fails-due into 4.x

In phpstan-deprecation-rules 2.x, the class.extendsDeprecatedClass check moved to the RestrictedClassNameUsageExtension mechanism. With PHPStan 2.x, this mechanism is only activated when a level is explicitly set. Without a level, it silently skips the check. Adding level: 0 restores detection of deprecated class extensions with no false positives.

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

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