fix(lint): fix ambiguity linter error in compio-io

[johnnyshields]

Surfaced during H2 PR test run:

error[E0034]: multiple applicable items in scope
  --> compio-io/tests/framed.rs:61:39
   |
61 |         self.0.get_ref().lock().await.flush().await
   |                                       ^^^^^ multiple `flush` found
   |
   = note: candidate #1 is defined in an impl of the trait `futures_util::SinkExt` for the type `T`
   = note: candidate #2 is defined in an impl of the trait `compio_io::AsyncWrite` for the type `std::vec::Vec<u8, A>`