Actually run doc tests in CI

rust-lang/cargo#6669

Author: mlafeldt

.github/workflows/rust.yaml

@@ -22,16 +22,16 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: build
-          args: --all-targets
+          args: --workspace
 
       - name: Lint
         uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: --all-targets -- -D warnings
+          args: --workspace -- -D warnings
 
       - name: Test
         uses: actions-rs/cargo@v1
         with:
           command: test
-          args: --all-targets --verbose
+          args: --workspace