Version Checks (indicate both or one)

• I have confirmed this bug exists on the lastest release of Linopy.

• I have confirmed this bug exists on the current master branch of Linopy.

Issue Description

When multiplying a variable or expression with a scalar numpy float, I receive a ValueError: different number of dimensions on data and dims: 0 vs 1.

Reproducible Example

import pandas as pd
from linopy import Model
import numpy as np

m = Model()
b = np.float64(5.0)
index = pd.Index(["a", "b", "c"], name="index")
m.add_variables(lower=0, name="var", coords=[index])
expr = m.variables["var"] * b

# workaround
expr = m.variables["var"] * b.item()

Expected Behavior

No ValueError in expr = m.variables["var"] * b

Installed Versions