fix: hash_root_file AttributeError: no field named 'to_numpy' (#1129)

With my installation
```
ROOT_HASH_CHECKS=on pytest
```
fails with errors like
```
FAILED src/Examples/Python/tests/test_examples.py::test_particle_gun - AttributeError: no field named 'to_numpy'
/cvmfs/sft.cern.ch/lcg/views/LCG_101/x86_64-centos7-gcc11-opt/lib/python3.9/site-packages/awkward/highlevel.py:1123: AttributeError
```
I'm using `LCG_101` which has Python 3.9 and `awkward` 1.0.2. It seems that `obj.to_numpy()` is not supported in this version, but `awkward.to_numpy(obj)` is.

Can someone advise whether this is likely OK for other installations?

Examples/Python/tests/helpers/hash_root.py

@@ -42,9 +42,9 @@ def hash_root_file(path: Path, ordering_invariant: bool = True) -> str:
                 for obj in row:
                     if isinstance(obj, ak.highlevel.Array):
                         if obj.ndim == 1:
-                            h.update(obj.to_numpy().tobytes())
+                            h.update(ak.to_numpy(obj).tobytes())
                         else:
-                            arr = ak.flatten(obj, axis=None).to_numpy()
+                            arr = ak.to_numpy(ak.flatten(obj, axis=None))
                             h.update(arr.tobytes())
                     else:
                         h.update(np.array([obj]).tobytes())