In-Place Operations (+=, -=, /=, *=) Yield Incorrect Units

While migrating Elephant to numpy >= 2.0 we discovered the following bug, where in place basic operations +=, -=, /= and *= result in incorrect units.

Minimal example to reproduce:
```python
a = 5 * pq.s
b = 6 * pq.kg

a /= b  # results incorrectly in a = 0.833 * s

a = a/b  # results in a = 0.833 * s/kg (expected)
```

With:
- Python 3.13.1
- quantities 0.16.1
