Add Cargo.toml to triggers for binary test builds (#9616)

Author: zanieb

.github/workflows/build-binaries.yml

@@ -14,8 +14,9 @@ on:
         type: string
   pull_request:
     paths:
-      # When we change pyproject.toml, we want to ensure that the maturin builds still work.
+      # When we change project metadata, we want to ensure that the maturin builds still work.
       - pyproject.toml
+      - Cargo.toml
       # And when we change this workflow itself...
       - .github/workflows/build-binaries.yml