Update heom 5b deadlink to resolve markdown test failure

Author: nwlambert

tutorials-v5/heom/heom-5b-fermions-discrete-boson-model.md

@@ -20,7 +20,7 @@ kernelspec:
 
 Here we model a single fermion coupled to two electronic leads or reservoirs (e.g.,  this can describe a single quantum dot, a molecular transistor, etc), also coupled to a discrete bosonic (vibronic) mode.
 
-Note that in this implementation we primarily follow the definitions used by Christian Schinabeck in his Dissertation https://opus4.kobv.de/opus4-fau/files/10984/DissertationChristianSchinabeck.pdf and related publications. In particular this example reproduces some results from https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.201407
+Note that in this implementation we primarily follow the definitions used by Christian Schinabeck in his Dissertation https://open.fau.de/items/36fdd708-a467-4b59-bf4e-4a2110fbc431 and related publications. In particular this example reproduces some results from https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.201407
 
 Notation: