Numba doesn't respect scalar types

### Description

Example revealed in #1406 

```python
import numpy as np
import pytensor.scalar as ps

x = ps.float64("x")
y = x.astype("float32")
y.eval({x: np.int64(0.0)}, mode="NUMBA").dtype  # AttributeError: 'float' object has no attribute 'dtype'
```