Don't run doctests.

Cargo detects the examples in the docstrings that aren't really examples (the
grammr specifications in `grammar.rs`).

Author: pmfirestone

.github/workflows/rust.yml

@@ -7,4 +7,4 @@ jobs:
     steps:
       - uses: actions/checkout@v5
       - name: Run tests
-        run: cargo test
+        run: cargo test --all-targets