Update flake, add update flake action

[sveitser]

Currently this fails to compile with

    Checking tide-disco v0.4.1 (/home/lulu/r/EspressoSystems/tide-disco)
error: future cannot be sent between threads safely
   --> src/socket.rs:227:19
    |
227 |               sink: Box::pin(sink::unfold(
    |  ___________________^
228 | |                 (conn.clone(), ty),
229 | |                 |(conn, accept), msg| async move {
230 | |                     conn.send(msg).await?;
231 | |                     Ok((conn, accept))
232 | |                 },
233 | |             )),
    | |______________^ future created by async block is not `Send`
    |
    = help: within `futures::sink::Unfold<(WebSocketConnection, MessageType), [closure@src/socket.rs:229:17: 229:38], [async block@src/socket.rs:229:39: 232:18]>`, the trait `std::marker::Send` is not implemented for `std::sync::MutexGuard<'_, SplitSink<WebSocketStream<tide::http_types::upgrade::Connection>, tide_websockets::Message>>`
note: future is not `Send` as this value is used across an await
   --> /home/lulu/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tide-websockets-0.4.0/src/websocket_connection.rs:35:37
    |
35  |         self.0.lock().send(message).await?;
    |         -------------               ^^^^^ - `self.0.lock()` is later dropped here
    |         |                           |
    |         |                           await occurs here, with `self.0.lock()` maybe used later
    |         has type `async_dup::MutexGuard<'_, SplitSink<WebSocketStream<tide::http_types::upgrade::Connection>, tide_websockets::Message>>` which is not `Send`
    = note: required for the cast from `Pin<Box<futures::sink::Unfold<(WebSocketConnection, MessageType), [closure@src/socket.rs:229:17: 229:38], [async block@src/socket.rs:229:39: 232:18]>>>` to `Pin<Box<(dyn futures::Sink<tide_websockets::Message, Error = SocketError<E>> + std::marker::Send + 'static)>>`

error: future cannot be sent between threads safely
   --> src/socket.rs:357:32
    |
357 |             Err(err) => return close(raw_conn, Err(err.into())).boxed(),
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: within `[async block@src/socket.rs:344:82: 353:6]`, the trait `std::marker::Send` is not implemented for `std::sync::MutexGuard<'_, SplitSink<WebSocketStream<tide::http_types::upgrade::Connection>, tide_websockets::Message>>`
note: future is not `Send` as this value is used across an await
   --> /home/lulu/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tide-websockets-0.4.0/src/websocket_connection.rs:35:37
    |
35  |         self.0.lock().send(message).await?;
    |         -------------               ^^^^^ - `self.0.lock()` is later dropped here
    |         |                           |
    |         |                           await occurs here, with `self.0.lock()` maybe used later
    |         has type `async_dup::MutexGuard<'_, SplitSink<WebSocketStream<tide::http_types::upgrade::Connection>, tide_websockets::Message>>` which is not `Send`
note: required by a bound in `futures::FutureExt::boxed`
   --> /home/lulu/.cargo/registry/src/index.crates.io-6f17d22bba15001f/futures-util-0.3.28/src/future/future/mod.rs:520:23
    |
518 |     fn boxed<'a>(self) -> BoxFuture<'a, Self::Output>
    |        ----- required by a bound in this associated function
519 |     where
520 |         Self: Sized + Send + 'a,
    |                       ^^^^ required by this bound in `FutureExt::boxed`

error: could not compile `tide-disco` (lib) due to 2 previous errors

[sveitser]

Oh I see just realized we don't have the lock file checked in here.