Fixing smart_ptrs_test GitHub CI failure. ``` File "/clif/build/clif/testing/python/smart_ptrs_test.py", line 41, in <module>   class AddPybind11(smart_ptrs_pybind11.Operation): AttributeError: 'NoneType' object has no attribute 'Operation' ``` Tested locally by temporarily setting ``` smart_ptrs_pybind11 = None ``` after the `import` block.
Fixing smart_ptrs_test GitHub CI failure.
```
File "/clif/build/clif/testing/python/smart_ptrs_test.py", line 41, in <module>
  class AddPybind11(smart_ptrs_pybind11.Operation):
AttributeError: 'NoneType' object has no attribute 'Operation'
```
Tested locally by temporarily setting
```
smart_ptrs_pybind11 = None
```
after the `import` block.

PiperOrigin-RevId: 360496631

google/clif,google/clif,google/clif