about: add a license

src/about.py

@@ -17,7 +17,7 @@
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-from gi.repository import Adw
+from gi.repository import Gtk, Adw
 
 developers = [
     "Roman Alifanov https://gitlab.eterfund.ru/ximper",
@@ -33,7 +33,8 @@ def build_about_dialog() -> Adw.AboutDialog:
         developer_name='Etersoft',
         version=tuneit_config.VERSION,
         developers=developers,
-        copyright='© 2024-2025 Etersoft'
+        copyright='© 2024-2025 Etersoft',
+        license_type=Gtk.License.GPL_3_0
     )
 
     # Translators: Replace "translator-credits" with your name/username, and optionally an email or URL.