Pin maybe-async-cfg to version 0.2.4 due to breaking changes.

With the configuration currently in master

> cargo build --all-features --release

Will use the latest `maybe-async-cfg` which is `0.2.5`.
This causes compilation errors.

This change pins the version to `=0.2.4` rather than attempting to upgrade to the latest version.
I'll leave that as an excersise to someone with more experience with maybe-async-cfg.

--
Details about the errors encountered:

Under Semantic Versioning (semver), a version change from 0.2.4 to 0.2.5 is considered a patch
release, which indicates that the update should contain only backwards-compatible bug fixes or minor
improvements. In other words, it shouldn't introduce breaking changes to existing functionality.

However, when 0.2.5 is selected we see the following compilation errors and many other similar ones:

```bash
error[E0277]: `Result<(), DisplayError>` is not a future
   --> src/size.rs:184:56
    |
184 |         Command::ComPinConfig(true, false).send(iface).await
    |                                                       -^^^^^
    |                                                       ||
    |                                                       |`Result<(), DisplayError>` is not a future
    |                                                       help: remove the `.await`
    |
    = help: the trait `Future` is not implemented for `Result<(), DisplayError>`, which is required by `Result<(), DisplayError>: IntoFuture`
    = note: Result<(), DisplayError> must be a future or must implement `IntoFuture` to be awaited
    = note: required for `Result<(), DisplayError>` to implement `IntoFuture`

error[E0119]: conflicting implementations of trait `size::DisplaySize` for type `size::DisplaySize128x64`
  --> src/size.rs:77:1
   |
77 | impl DisplaySize for DisplaySize128x64 {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   | |
   | first implementation here
   | conflicting implementation for `size::DisplaySize128x64`
error[E0277]: the trait bound `size::DisplaySize128x32: DisplaySizeAsync` is not satisfied
  --> src/mode/terminal.rs:48:30
   |
48 | impl TerminalDisplaySize for DisplaySize128x32 {
   |                              ^^^^^^^^^^^^^^^^^ the trait `DisplaySizeAsync` is not implemented for `size::DisplaySize128x32`
   |
help: this trait has no implementations, consider adding one
  --> src/size.rs:33:1
   |
33 | pub trait DisplaySize {
   | ^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `TerminalDisplaySizeAsync`
  --> src/mode/terminal.rs:23:32
   |
23 | pub trait TerminalDisplaySize: DisplaySize {
   |                                ^^^^^^^^^^^ required by this bound in `TerminalDisplaySizeAsync`
```

Cargo.toml

@@ -24,7 +24,7 @@ display-interface-i2c = "0.5.0"
 display-interface-spi = "0.5.0"
 embedded-graphics-core = { version = "0.4.0", optional = true }
 embedded-hal-async = { version = "1.0.0",  optional = true }
-maybe-async-cfg = "0.2.4"
+maybe-async-cfg = "=0.2.4"
 
 [dev-dependencies]
 embedded-graphics = "0.8.0"