github: use actions-rs/cargo instead of run

From https://github.com/actions-rs/cargo#use-cases, it sounds like
errors may be presented in a nicer way if we use `actions-rs/cargo`
instead of a simple `run`, so let's try it.

.github/workflows/build.yml

@@ -22,11 +22,15 @@ jobs:
         override: true
         profile: minimal
     - name: Build
-      run: |
-        cargo build --workspace --verbose
+      uses: actions-rs/cargo@v1
+      with:
+        command: build
+        args: --workspace --verbose
     - name: Test
-      run: |
-        cargo test --workspace --verbose
+      uses: actions-rs/cargo@v1
+      with:
+        command: test
+        args: --workspace --verbose
       env:
         RUST_BACKTRACE: 1