panic in publish job due to libsyntax rename

[calebcartwright]

The most recent publish job failed with a

thread 'main' panicked at 'failed to execute cargo: Os { code: 2, kind: NotFound, message: "No such file or directory" }', 

error, and I believe that's because libsyntax appears to have been renamed to librustc_ast.

Refs: rust-lang/rust#69592

I'll open a PR to update the script to reflect that change , though it looks like we may potentially need to add some additional crates to the publish list for rustfmt (looks like libsyntax was split into multiple crates in addition to the rename)

cc @topecongiro

Edit: looks it was just the rename of libsyntax, no additional crate splitting