Actions: Build before formatting check

cargo fmt does not build the code, and running it in a fresh clone of
the codebase will fail because the protobuf code has not been generated.

.github/workflows/rust.yml

@@ -14,6 +14,14 @@ jobs:
           toolchain: 1.37.0
           override: true
 
+      # cargo fmt does not build the code, and running it in a fresh clone of
+      # the codebase will fail because the protobuf code has not been generated.
+      - name: cargo build
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --all
+
       # Ensure all code has been formatted with rustfmt
       - run: rustup component add rustfmt
       - name: Check formatting