"Death saving throws" are just another saving throw
This specific kind of saving throws has a few unique rules and such, but in the end it's just another saving throw, which falls under the tag of the same name. If we were to make a tag for every mechanic that is part of a larger category, but with a few specific rules for it, there would be no end to the tags which need to be created (which would pretty much defeat the point of tags in the first place).
As such, I believe the tag saving-throw should do the trick, just like it currently does for other saving throws. As a matter of fact, it would even make sense to edit this tag's description to include those throws, as just about every other kind of throw is listed there.