security/doas: update to version 6.2p4

Changelog picked from https://github.com/slicer69/doas/releases:

6.2p4:
* Keeping environment variables with keepenv
  On some platforms (seemingly Linux and macOS) it is possible for
  repeated calls to getpwuid() can over-write the original struct
  passwd structure. (This behaviour may vary depending on which
  C library is used. This can lead to the original user's
  environment data being overwritten by the target user's, even
  when "keepenv" is specified in the doas.conf file.
  We now do a deep copy of the original and target users' struct
  passwd information to avoid over-writing the original on platforms
  where libc uses a static area for all calls.

(ng0)