portal: Add g_autoptr() defines for old GLib versions

We don't need to check for GLib 2.44 (the first release with g_autoptr()
support) since Flatpak requires that version in configure.ac.

Fixes https://github.com/flatpak/flatpak/issues/3403
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f