Make `beta` in partitioned heat conduction tutorial consistent with paper

[BenjaminRodenberg]

For some reason our tutorial here uses beta = 1.3:

tutorials/partitioned-heat-conduction/fenics/heat.py

Line 70 in 6023dbd

beta = 1.3 # parameter beta

However, the FEniCS tutorial book, p.41 and the quasi-Newton paper uses beta = 1.2. To make things consistent, we should change the value here.

[BenjaminRodenberg]

Also important: This change is also required for the nutils and OpenFOAM versions of this case.

[BenjaminRodenberg]

Closed this issue via #379.

[BenjaminRodenberg]

Marking this issue as a bug. I want to backport this fix and release it as a bugfix release via #558. Main motivation: consistency in results and literature when comparing the distributions for preCICE v2 and v3.