Parent class modifications are lost when both parent and child are modified via Extension

[abevol]

Description

• Using Extension to modify both a parent class and its subclass will cause the modifications to the parent class to become completely ineffective.
• The call order of install_script_extension does not affect the result — the modifications to the parent class always become ineffective.
• The modifications to the subclass remain effective.
• No error log.
• If one side or both are modified through Hook instead, this issue will not occur.

Environment

• OS: Windows 11
• Game: Dome Keeper
• Game Engine: godotsteam v4.2.2