Pin Rust version in CI workflows to 1.67

.github/workflows/test-python.yaml

@@ -43,6 +43,9 @@ jobs:
         with:
           toolchain: stable
 
+      - name: "Set default Rust version to 1.67.0"
+        run: rustup default 1.67.0
+
       - name: "Install requirements"
         run: ${PYBIN}/pip install -r requirements.txt