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/google.golang.org/grpc/attributes/attributes.go

@@ -25,6 +25,11 @@
 // later release.
 package attributes
 
+import (
+	"fmt"
+	"strings"
+)
+
 // Attributes is an immutable struct for storing and retrieving generic
 // key/value pairs.  Keys must be hashable, and users should define their own
 // types for keys.  Values should not be modified after they are added to an
@@ -99,3 +104,27 @@ func (a *Attributes) Equal(o *Attributes) bool {
 	}
 	return true
 }
+
+// String prints the attribute map. If any key or values throughout the map
+// implement fmt.Stringer, it calls that method and appends.
+func (a *Attributes) String() string {
+	var sb strings.Builder
+	sb.WriteString("{")
+	first := true
+	for k, v := range a.m {
+		var key, val string
+		if str, ok := k.(interface{ String() string }); ok {
+			key = str.String()
+		}
+		if str, ok := v.(interface{ String() string }); ok {
+			val = str.String()
+		}
+		if !first {
+			sb.WriteString(", ")
+		}
+		sb.WriteString(fmt.Sprintf("%q: %q, ", key, val))
+		first = false
+	}
+	sb.WriteString("}")
+	return sb.String()
+}