imports: add 'UnixOS' list of Unix-like systems
imports: add 'UnixOS' list of Unix-like systems

From Go 1.19, the build constraint 'unix' proposed in golang/go#20322 is
satisfied by any sufficiently Unix-like value of GOOS, as defined by
src/go/build/syslist.go. This commit adds a 'UnixOS' list containing the
values of GOOS that would satisfy the 'unix' constraint in Go 1.19.

Co-authored-by: Paul Jolly <a027184a55211cd23e3f3094f1fdc728df5e0500@myitcv.io>

rogpeppe/go-internal