Upgrade rust toolchain

See [1] for details.

Some floating point intrinsics were added in this newer version which
helps on systems where these intrinsics are not provided by avr-gcc.

[1]: Rahix/avr-hal#651

Author: Rahix

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Install Nightly Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
-          toolchain: nightly-2025-03-03
+          toolchain: nightly-2025-04-27
           components: rustfmt,rust-src
 
       # Actual test run
@@ -60,7 +60,7 @@ jobs:
       - name: Install Rust
         uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
-          toolchain: nightly-2025-03-03
+          toolchain: nightly-2025-04-27
           rustflags: ""
           components: rust-src,rustfmt
       - name: Install AVR gcc, binutils, and libc

examples/atmega328p/rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
-channel = "nightly-2025-03-03"
+channel = "nightly-2025-04-27"
 components = ["rust-src"]
 profile = "minimal"