TH2M throws error with embedded fracture permeability model
### Description
As reported by @kuateric , TH2m process seems to have trouble with using the embeddedfracture Permeability model which supposedly worked in the past with TH2M, so recent changes seem to have broken something.
## Steps to Reproduce the Problem
To reproduce the error, take the benchmark `Tests/Data/TH2M/HM/flow_fully_saturated.prj` and exchange the permeability property with:
```xml
<property>
<name>permeability</name>
<type>EmbeddedFracturePermeability</type>
<intrinsic_permeability>6.6e-21</intrinsic_permeability>
<initial_aperture>0</initial_aperture>
<mean_frac_distance>0.01</mean_frac_distance>
<threshold_strain>1e-4</threshold_strain>
<fracture_normal>1 0 0</fracture_normal>
<fracture_rotation_xy>zero</fracture_rotation_xy>
<fracture_rotation_yz>zero</fracture_rotation_yz>
</property>
```
and add a zero parameter.
**Expected behavior:** Simulation executes.
**Actual behavior:** An error is thrown: `error: std::get: wrong index for variant`
The error happens in the integration loop of TH2M at ```models.permeability_model.eval(``` (L. 217)
But I am not capable of debugging this any further. @endJunction maybe you can help?
## Specifications
- Version: 6.5.4
- Platform: Ubuntu 22.04.4 via WSL
issue