deps: update buildkit, vendor changes

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

vendor/golang.org/x/crypto/ssh/common.go

@@ -10,7 +10,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"strings"
 	"sync"
 
 	_ "crypto/sha1"
@@ -128,6 +127,14 @@ func isRSA(algo string) bool {
 	return contains(algos, underlyingAlgo(algo))
 }
 
+func isRSACert(algo string) bool {
+	_, ok := certKeyAlgoNames[algo]
+	if !ok {
+		return false
+	}
+	return isRSA(algo)
+}
+
 // supportedPubKeyAuthAlgos specifies the supported client public key
 // authentication algorithms. Note that this doesn't include certificate types
 // since those use the underlying algorithm. This list is sent to the client if
@@ -140,8 +147,6 @@ var supportedPubKeyAuthAlgos = []string{
 	KeyAlgoDSA,
 }
 
-var supportedPubKeyAuthAlgosList = strings.Join(supportedPubKeyAuthAlgos, ",")
-
 // unexpectedMessageError results when the SSH message that we received didn't
 // match what we wanted.
 func unexpectedMessageError(expected, got uint8) error {