doas: 6.0 -> 6.6.1

https://github.com/Duncaen/OpenDoas/compare/v6.0...v6.6.1

There are a decent chunk of changes in there. I'm mostly interested in
5debef098b7ebba67da5db9fbb020a7cd0f90a7f, which fixes the parsing of
/proc/$pid/stat that is used to implement timestamping.