build: Fix beta clippy issue (useless_vec)

warning: useless use of `vec!`
   --> test_infra/src/lib.rs:111:30
    |
111 |             let mut events = vec![epoll::Event::new(epoll::Events::empty(), 0); 1];
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: you can use an array directly: `[epoll::Event::new(epoll::Events::empty(), 0); 1]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_vec
    = note: `#[warn(clippy::useless_vec)]` on by default

Signed-off-by: Yu Li <liyu.yukiteru@bytedance.com>

vmm/src/serial_manager.rs

@@ -229,7 +229,7 @@ impl SerialManager {
                     const EPOLL_EVENTS_LEN: usize = 3;
 
                     let mut events =
-                        vec![epoll::Event::new(epoll::Events::empty(), 0); EPOLL_EVENTS_LEN];
+                        [epoll::Event::new(epoll::Events::empty(), 0); EPOLL_EVENTS_LEN];
 
                     loop {
                         let num_events = match epoll::wait(epoll_fd, timeout, &mut events[..]) {