Pin Rust to 1.82.

We have deny(warnings) and 1.83 has new warnings. I'll fix these
properly later.

.github/workflows/build.yml

@@ -19,8 +19,10 @@ jobs:
 
       - name: Install targets
         run: |
-          rustup target add thumbv7em-none-eabihf
-          rustup component add rust-src
+          rustup install 1.82
+          rustup default 1.82
+          rustup target add thumbv7em-none-eabihf --toolchain=1.82
+          rustup component add rust-src --toolchain=1.82
 
       - name: Find slug name
         run: |