Unable to hide titlebar from flatpak apps.

[AyrtonAlbuquerque]

Describe the bug
I noticed that flatpak apps do not have their titlebars hidden when maximized (vscode, pycharm, gitkraken, and many others)

To Reproduce
Steps to reproduce the behavior:

1. install a flatpak app like vscode
2. configure Unite to hide titlebar on maximized windows
3. See the problem

Expected behavior
When configured to hide titlebar of maximized windows, hide them, no matter the installation method.

Environment (please complete the following information):

• OS: Ubuntu 26.04, Ubuntu 24.04
• GNOME Shell version 46, 50
• Unite version 85