test-groundwater-deep exceeds SML when run with coverage build

See test/dai-system-tests/tests/daisy/lower_boundary/test-groundwater-deep.dai

The difference is observed for a coverage build on Linux using gcc. 

```
soil_water.dlf
	[Matrix to biopores]: 72.633 | 73.8315 | 1.19850000000001 millimeter | 1 millimeter
	[Biopores to matrix]: 72.633 | 73.8315 | 1.19850000000001 millimeter | 1 millimeter

```