try gnome 50 runtime

Author: rmartin16

src/briefcase/bootstraps/toga.py

@@ -191,7 +191,7 @@ def pyproject_table_linux_appimage(self):
     def pyproject_table_linux_flatpak(self):
         return """\
 flatpak_runtime = "org.gnome.Platform"
-flatpak_runtime_version = "49"
+flatpak_runtime_version = "50"
 flatpak_sdk = "org.gnome.Sdk"
 """