Pin Rust version to 1.66.1

This fixes an issue with Rust 1.67.0 and littlefs2, see:
	https://github.com/trussed-dev/littlefs2/issues/26

.github/workflows/ci.yml

@@ -20,11 +20,9 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Install Rust toolchain
-        uses: actions-rs/toolchain@v1
-        with:
-          toolchain: stable
-          target: ${{ matrix.target }}
-          profile: minimal
+        run: |
+          rustup show
+          rustup target add ${{ matrix.target }}
 
       - name: Install build dependencies
         run: >

.github/workflows/firmwares.yml

@@ -32,14 +32,11 @@ jobs:
         with:
           release: "10-2020-q4"
 
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          target: thumbv8m.main-none-eabi
-          override: true
-          components: llvm-tools-preview
-
+      - name: Install rustup toolchain
+        run: |
+          rustup show
+          rustup component add llvm-tools-preview
+          rustup target add thumbv8m.main-none-eabi
 
       - name: cargo install cargo-binutils
         uses: actions-rs/install@v0.1

rust-toolchain.toml

@@ -0,0 +1,4 @@
+[toolchain]
+channel = "1.66.1"
+profile = "minimal"
+components = ["rustfmt", "clippy"]