Fix async callbacks for CUDA Python
Fix async callbacks for CUDA Python

CUDA Python test results are now:

```
Ran 1201 tests in 73.923s

FAILED (failures=1, errors=9, skipped=10, expected failures=2)
```

seibert/numba,seibert/numba,seibert/numba,IntelLabs/numba,numba/numba,IntelLabs/numba,cpcloud/numba,cpcloud/numba,numba/numba,seibert/numba,numba/numba,IntelLabs/numba,cpcloud/numba,cpcloud/numba,IntelLabs/numba,seibert/numba,numba/numba,numba/numba,cpcloud/numba,IntelLabs/numba