test-avr: use nightly 2022-09-23

Author: dhardy

.github/workflows/test.yml

@@ -166,8 +166,9 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Install toolchain
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@master
         with:
+            toolchain: nightly-2022-09-23 # https://github.com/rust-lang/rust/issues/102278
             components: rust-src
       - name: Build top-level only
         run: cargo build -Z build-std=core --target=avr-unknown-gnu-atmega328 --no-default-features