Fix unused variable warning when field of adjacently tagged enum is skipped

[arilotter]

Replace skip_seralizing tuple members with _ in generated serializer.
I'm not totally convinced this is the right solution, since it requires creating 2x the Vecs, but it's the most "correct" solution I've found.

[dtolnay]

Thanks! I am concerned how much this change makes the implementation of this function harder to read and understand. How about simply putting #[allow(unused_variables)] on the let statement, with a comment?

[arilotter]

I agree! I wrote a message in the #serde irc channel asking if #[allow(unused_variables)] was the way to go, but I thought I'd try without it in case y'all wanted to avoid that :)

I'm very happy to make the fix a simple warning suppression, now my project will finally compile with no warnings :D 🙏

[dtolnay]

Thanks!