[Gtk-osx-users] trivial warning fix (typo)

[Antoine M. <an...@na...>]

A small typo in ./Source/jhbuild/modulesets/gtk-osx-gstreamer.modules,
(stable) is causing this warning:
W: skipped hash check (missing support for
sha256a9d801c3d42b456a6ebc0b95f68c44f153f756ec0fbd4877197c469cc67771fa)

Should obviously be:
sha256:a9d801c3d42b456a6ebc0b95f68c44f153f756ec0fbd4877197c469cc67771fa

Cheers
Antoine