Rock/Pop Anne Murray: ''A Little Good News'' (EMI/Capitol ST-12301). One can't fault Anne Murray's splendid voice - brimming with enough sincerity, usually, to fill every song - and her pleasant-enough selection of material. Added together, though, they don't equal the sum of the parts on ''A Little Good News.'' It's an agreeable LP, but a shallow effort. Hardly a cut here is less than masterfully sung; the voice, certainly, is as affecting as ever. But with a couple of modest exceptions, there's little that sounds more than routine. The title song, ''A Little Good News,'' is good enough. It's topical and timeless in its quest for less mayhem and more ho-hum. ''That's Not the Way (It's S'posed to Be)'' builds up a little bit of a certain quality that, for lack of a better word, I'll just call musical excitement. Yet, that's at a premium here. Murray's lack of pop-star pretension and the country-rich beauty of her voice appeal greatly. Sad to say, these don't quite elevate this album of merely pleasant music.