[Jammy, Focal] fusiondirectory installation issue: fatal error encountered

[Federico Quattrin]

When installing the package as stated in https://fusiondirectory-user-manual.readthedocs.io/en/1.3/fusiondirectory/install/debian/debian-fd-install.html, I encountered an error in the setup page: Fatal Error: "Class SetAttribute cannot extend final class Attribute" in /usr/share/fusiondirectory/include/simpleplugin/attributes/class_SetAttribute.inc on line 0.

Here are the commands I'm executing:

1. `sudo apt-get install fusiondirectory`
2. `sudo apt-get install fusiondirectory-schema`

Then I executed `sudo fusiondirectory-insert-schema` successfully. After that, when I attempt to access localhost/fusiondirectory I receive the fatal error.

Steps to reproduce:
1. Run `sudo apt update && sudo apt -y upgrade`
2. Run `sudo apt-get install fusiondirectory`
3. Run `sudo apt-get install fusiondirectory-schema`
4. Run `sudo fusiondirectory-insert-schema`
5. Run `curl -L localhost/fusiondirectory`

You will see the fatal error in the HTTP response.

I'm encountering this issue in Focal with fusiondirectory 1.3-2 and in Jammy with fusiondirectory 1.3-4build1