Bump rustc-ap crates to version 706

[thomaseizinger]

This is a follow-up from bumping the crates to version 706 in rustfmt: rust-lang/rustfmt#4694

[kngwyu]

Thanks!
Do we need the release corresponding to this change?

[thomaseizinger]

Thanks!
Do we need the release corresponding to this change?

Not from my side no and I think @calebcartwright wants to wait with another release dance until next week :)

[calebcartwright]

@kngwyu - yes we'll need a release, but it's not terribly urgent (no broken toolstate this time) so whenever you can get around to it would be great!