Use latest nightly for fmt of async

Author: Ulf Lilleengen

.github/workflows/rustfmt.yml

@@ -21,5 +21,16 @@ jobs:
         with:
           command: fmt
           args: --all -- --check
+  fmt-async:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          override: true
+          components: rustfmt
       - run: cargo fmt --all -- --check
         working-directory: embedded-nal-async