chore: Update pyo3 to new API (#852)

Author: simoncozens

Cargo.lock

@@ -46,8 +46,8 @@ log = "0.4.14"
 itertools = "0.15.0"
 
 # Fontbakery bridge / Python module. Keep these two together
-pyo3 = "0.25"
-pythonize = "0.25"
+pyo3 = "0.29"
+pythonize = "0.29"
 
 indexmap = { version = "2", features = ["serde"] }
 tabled = "0.21.0"

Cargo.toml

@@ -91,7 +91,7 @@ impl CheckTester {
             .get_item(0)
             .map_err(|_| PyValueError::new_err("No args found"))?;
         let testables = if first_arg.is_instance_of::<PyList>() {
-            let first_arg: &Bound<PyList> = first_arg.downcast()?;
+            let first_arg: &Bound<PyList> = first_arg.cast()?;
             first_arg
                 .iter()
                 .map(|a| obj_to_testable(py, &a))