Update toolchain to nightly

Signed-off-by: Arjo Chakravarty <arjoc@google.com>

.github/workflows/rust.yml

@@ -16,6 +16,12 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
+    - name: Install latest nightly
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: nightly
+            override: true
+            components: rustfmt, clippy
     - name: Build
       run: cargo build --verbose
     - name: Run tests