Update go.mod and vendor

vendor/github.com/moby/buildkit/frontend/result.go

@@ -1,25 +0,0 @@
-package frontend
-
-import (
-	"github.com/moby/buildkit/solver"
-)
-
-type Result struct {
-	Ref      solver.ResultProxy
-	Refs     map[string]solver.ResultProxy
-	Metadata map[string][]byte
-}
-
-func (r *Result) EachRef(fn func(solver.ResultProxy) error) (err error) {
-	if r.Ref != nil {
-		err = fn(r.Ref)
-	}
-	for _, r := range r.Refs {
-		if r != nil {
-			if err1 := fn(r); err1 != nil && err == nil {
-				err = err1
-			}
-		}
-	}
-	return err
-}