Update embassy-time and embassy-sync revisions in

[danbev]

This commit updates the revision of embassy-time and embassy-sync in infra/pre-provision to fix the following compilation error:

error[E0107]: this struct takes 1 generic argument but 2 generic arguments were supplied
  --> /.cargo/git/checkouts/btmesh-e14acedbce757b27/6840160/btmesh-device/src/lib.rs:34:27
   |
34 |     embassy_sync::signal::Signal<embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex, T>;
   |                           ^^^^^^ expected 1 generic argument                                 - help: remove this generic argument
   |
note: struct defined here, with 1 generic parameter: `T`
  --> /.cargo/git/checkouts/embassy-9312dcb0ed774b29/3b58ac1/embassy-sync/src/signal.rs:31:12
   |
31 | pub struct Signal<T> {
   |            ^^^^^^ -

For more information about this error, try `rustc --explain E0107`. error: could not compile `btmesh-device` due to previous error

The commit also adds a rust-toolchain.toml to configure nightly rustc as currently there a number of compilation errors like the following two:

error[E0658]: generic associated types are unstable
   --> /.cargo/git/checkouts/embassy-9312dcb0ed774b29/b7d0944/embassy-sync/src/pipe.rs:450:9
    |
450 | /         type FlushFuture<'a> = impl Future<Output = Result<(), Self::Error>>
451 | |         where
452 | |             Self: 'a;
    | |_____________________^
    |
    = note: see issue #44265 <https://github.com/rust-lang/rust/issues/44265> for more information
    = help: add `#![feature(generic_associated_types)]` to the crate attributes to enable

error[E0658]: where clauses on associated types are unstable
   --> /.cargo/git/checkouts/embassy-9312dcb0ed774b29/b7d0944/embassy-sync/src/pipe.rs:450:9
    |
450 | /         type FlushFuture<'a> = impl Future<Output = Result<(), Self::Error>>
451 | |         where
452 | |             Self: 'a;
    | |_____________________^
    |
    = note: see issue #44265 <https://github.com/rust-lang/rust/issues/44265> for more information
    = help: add `#![feature(generic_associated_types)]` to the crate attributes to enable

   Compiling cargo_metadata v0.15.0
For more information about this error, try `rustc --explain E0658`.
error: could not compile `embassy-sync` due to 18 previous errors
warning: build failed, waiting for other jobs to finish...

[lulf]

Thanks @danbev !