Enable non-strict mode for LIV in the validator competition

This adds a flag to LIV telling it that it should not expect witnesses to contain a full, inductive proof. In this mode we will output unknown(false) instead of false in case we find one of the generated conditions to be violated.

Depends on sosy-lab/benchmarking/fm-tools!192 (merged) for the new DOI with a version of LIV that supports this option.