Resolve cargo clippy errors

Here was the error.

```
❯ cargo clippy
    Checking veilid-tools v0.2.5 (~/Developer/veilid/veilid-tools)
error: this `MutexGuard` is held across an `await` point
   --> veilid-tools/src/tests/common/test_host_interface.rs:269:17
    |
269 |             let mut tick = tick_1.lock();
    |                 ^^^^^^^^
    |
    = help: consider using an async-aware `Mutex` type or ensuring the `MutexGuard` is dropped before calling await
note: these are all the `await` points this lock is held through
   --> veilid-tools/src/tests/common/test_host_interface.rs:271:25
    |
271 |             sleep(1000).await;
    |                         ^^^^^
...
274 |             sleep(1000).await;
    |                         ^^^^^
...
277 |             sleep(1000).await;
    |                         ^^^^^
...
280 |             sleep(1000).await;
    |                         ^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#await_holding_lock
note: the lint level is defined here
   --> veilid-tools/src/lib.rs:23:9
    |
23  | #![deny(clippy::all)]
    |         ^^^^^^^^^^^
    = note: `#[deny(clippy::await_holding_lock)]` implied by `#[deny(clippy::all)]`

error: could not compile `veilid-tools` (lib) due to previous error
```

veilid-tools/src/tests/common/test_host_interface.rs

@@ -259,6 +259,7 @@ pub async fn test_interval() {
     stopper.await;
 }
 
+#[allow(clippy::await_holding_lock)]
 pub async fn test_timeout() {
     info!("testing timeout");