P5: Add isVirtual() to parity test getters (PHP 8.4)

[devin-ai-integration]

Add isVirtual() to the getGettersToCheck() array in ReflectionPropertyTest.php for the PHP 8.4 block. This ensures the parity test compares isVirtual() output between parser-reflection and native reflection for all test stub properties.

Part of #162

[devin-ai-integration]

Completed in the PHP 8.3/8.4 parity work (Waves 1-5).