Chore: Backslash character in test data causes pronto to have error

Currently have to downgrade pronto to <2.6 because of line 3705 below

https://github.com/INCATools/ontology-access-kit/blob/aaede8e497e98fe7677e82730eeb56039241ac3b/tests/input/interneuron.obo#L3704-L3706

It can't handle a backslash in while parsing the file. Interested to know if this is a format error in the obo file or a bug in pronto.

Start with tests/input/interneuron.obo around lines 3704-3706 and reproduce parsing it with pronto 2.6 or later. Check whether the backslash is valid OBO syntax or exposes a pronto parsing bug; done means documenting the cause and resolving the incompatibility with a focused regression test or confirmed format correction.

Written by the indexing model from the issue text.