Update gomod and vendor

vendor/github.com/moby/buildkit/source/git/gitsource_unix.go

@@ -0,0 +1,35 @@
+// +build !windows
+
+package git
+
+import (
+	"context"
+	"os/exec"
+	"syscall"
+	"time"
+)
+
+func runProcessGroup(ctx context.Context, cmd *exec.Cmd) error {
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	if err := cmd.Start(); err != nil {
+		return err
+	}
+	waitDone := make(chan struct{})
+	go func() {
+		select {
+		case <-ctx.Done():
+			syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM)
+			go func() {
+				select {
+				case <-waitDone:
+				case <-time.After(10 * time.Second):
+					syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
+				}
+			}()
+		case <-waitDone:
+		}
+	}()
+	err := cmd.Wait()
+	close(waitDone)
+	return err
+}