Missing transition (E->I) in ODE SEIR benchmark

### Bug description

in `flow_simulation_ode_seir.cpp`, there is no flow from S -> E...

### Version

Any

### To reproduce

in script

### Relevant log output

```zsh

```

### Add any relevant information, e.g. used compiler, screenshots.

```zsh

```

### Checklist

- [x] Attached labels, especially loc:: or model:: labels.
- [x] Linked to project