Error in one Diet Planning code line

**Description**
[Diet Planning example](https://docs.ocean.dwavesys.com/en/stable/examples/hybrid_cqm_diet.html) line
```
quantities[0] * quantities[1]
```
needs to be updated to use non-real quantities

**To Reproduce**
```
>>> quantities[0] * quantities[1]
...
ValueError: REAL variables (e.g. 'rice') cannot have interactions
```

**Expected behavior**
Use the int variables or note the error

**Environment:**
- OS: WIN10
- Python version: 3.9
- Ocean SDK version: 6.9.0

**Additional context**
Reported by user