Infeasible constraint ignored

[MiftariB]

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

The infeasible constraints that only use parameters are ignored by the solving phase that returns that the solution is optimal.

Reproducible Example

import linopy 

model = linopy.Model()
x = model.add_variables([0], [10], name="x")
model.add_constraints(linopy.LinearExpression(12, model)==linopy.LinearExpression(13, model))
model.add_objective(x, "minimize")
model.solve()

Expected Behavior

It should return infeasible

Installed Versions

Details

linopy 0.5.8

[RobbieKiwi]

The constraint that you make there is saying that 12 should equal 13 which is a bit strange. The fact that you can make such a constraint in the first place is an issue that I try to address in this pr