style(bindings): fix new clippy lint

[jmayclin]

Description of changes:

Address the new clippy lint

    Checking s2n-tls v0.2.4 (/home/runner/work/s2n-tls/s2n-tls/bindings/rust/s2n-tls)
error: assigning the result of `Clone::clone()` may be inefficient
   --> s2n-tls/src/connection.rs:717:21
    |
717 |                     *prev_waker = waker.clone();
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `clone_from()`: `prev_waker.clone_from(waker)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#assigning_clones
    = note: `-D clippy::assigning-clones` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::assigning_clones)]`

Testing:

CI should pass
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