GNOME 43: separate webkit2gtk-5.0.bst from webkitgtk.inc and hold it to WebKitGTK 2.38
In March 2023, when WebKitGTK 2.40 is released, we'll want to update users from 2.38 -> 2.40 so they can continue to get CVE fixes. This is what we usually do.
But this time around, we don't want to update webkit2gtk-5.0.bst, since it will be changing API version. It should probably stop depending on webkitgtk.inc altogether, but only in the gnome-43 branch.