GtkSourceView branching

[Christian Hergert <christian hergert me>]

GNOMErs,

A new gtksourceview-4-6 branch has been created which will be used to
release the final GTK 3 series (gtksourceview-4.6.x) of GtkSourceView.
This branch will continue to get updates for the foreseeable future (or
rather, the realistic lifetime of GTK 3 libraries).

Next week I plan to land the GTK 4 port of GtkSourceView to master which
will include a major version number change.

If you're using GtkSourceView from a Flatpak manifest in your Nightly
builds you probably want to update your manifest to include a branch
name like:

{
    "name" : "gtksourceview",
    "buildsystem" : "meson",
    "sources" : [
        {
            "type" : "git",
            "url" : "https://gitlab.gnome.org/GNOME/gtksourceview.git";,
            "branch" : "gtksourceview-4-6"
        }
    ]
},

Stable release Flatpaks should continue using a tag identifier like
you've been doing (such as "4.4.0", etc).

Thanks for your attention!

-- Christian