Pull Request resolves #47635.

• I read the Generative AI policy and my contribution is either not created with the help of AI or is compatible with the policy and GNU/GPL 2 or later.

Summary of Changes

Load the extension mainfest file to create the class from the correct extension_root parameter as source is only compiled once.

Testing Instructions

• Extract the file plg_system_test1.zip into the folder /plugins/system/test1
• Extract the file plg_system_test2.zip into the folder /plugins/system/test2
• Discover install the extensions

Actual result BEFORE applying this Pull Request

The following info text is displayed:
Postflight executed for test 1

Expected result AFTER applying this Pull Request

The following info text is displayed:
Postflight executed for test 1
Postflight executed for test 2

Link to documentations

Please select:

• Documentation link for guide.joomla.org:

• No documentation changes for guide.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed