Update c/image for golang.org/x/exp

> go get github.com/containers/image/v5@main
> go mod tidy && go mod vendor

This updates c/image with a new version of x/exp.
That package has changed API in an incompatible way,
so just bumping x/exp (as in https://github.com/containers/skopeo/pull/2060 )
would break Skopeo builds.

This updates both c/image and x/exp in lockstep (and nothing
needs updating in Skopeo itself for the x/exp breakage).

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/github.com/go-openapi/errors/api.go

@@ -112,7 +112,7 @@ func flattenComposite(errs *CompositeError) *CompositeError {
 	for _, er := range errs.Errors {
 		switch e := er.(type) {
 		case *CompositeError:
-			if len(e.Errors) > 0 {
+			if e != nil && len(e.Errors) > 0 {
 				flat := flattenComposite(e)
 				if len(flat.Errors) > 0 {
 					res = append(res, flat.Errors...)