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It says nothing in the Monster Manual, but they are undead and I seem to recall that being a thing in previous editions.

No, ghouls and ghasts are not vulnerable to sunlight

Nothing in the monster entries for ghouls or ghasts mentions any kind of sensitivity or vulnerability to sunlight, and there are no universally applicable rules which would imply as much. We only note that "ghouls roam the night in packs", from which we can infer that these kinds of creatures are primarily nocturnal - which would make sense for a creature which can see in the dark, giving it an advantage over most of its humanoid prey.

Many magical effects which are thematically based on sunlight - such as the spell Sunbeam - are especially effective against undead creatures, so you could construe that as a kind of vulnerability to sunlight which is shared amongst all undead. Ordinarily, though, ghouls/ghasts are not hindered by lighting of any kind.

I'm not sure where you got the impression these monsters were vulnerable to sunlight in earlier editions. There's no mention of such a weakness in the 3.5e ghoul/ghast entry or the general undead traits, nor in the 1e AD&D Monster Manual entries for them.