avoid integer overflow in StopTime for borehole model

[mwetter]

This issue is to change:

IBPSA/Fluid/Geothermal/Borefields/Validation/ConstantHeatInjection_100Boreholes.mo
...
-  annotation (experiment(Tolerance=1e-6, StopTime=31536000000),
+  annotation (experiment(Tolerance=1e-6, StopTime=31536.0E+06),

as the first notation causes an integer overflow in the CI testing for JModelica. (The maximum value for an integer is 2147483647.)

[MassimoCimmino]

@mwetter I was not aware of this. Should the unit test page on the wiki be updated to specify that StartTime and StopTime be given as float regardless of their values (or if non-zero) to avoid errors in the future?

[mwetter]

@MassimoCimmino : I will update BuildingsPy to catch overflow if specified as an integer. This is more robust than trusting that users follow the coding guideline.