build: Bump version to 2.61.0
build: Bump version to 2.61.0

Ready for the new unstable release series.

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib