Bump github.com/containers/storage from 1.15.8 to 1.16.0

Bumps [github.com/containers/storage](https://github.com/containers/storage) from 1.15.8 to 1.16.0.
- [Release notes](https://github.com/containers/storage/releases)
- [Changelog](https://github.com/containers/storage/blob/master/docs/containers-storage-changes.md)
- [Commits](https://github.com/containers/storage/compare/v1.15.8...v1.16.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

vendor/github.com/mattn/go-shellwords/util_windows.go

@@ -1,4 +1,4 @@
-// +build windows,go1.6
+// +build windows
 
 package shellwords
 
@@ -10,7 +10,10 @@ import (
 )
 
 func shellRun(line, dir string) (string, error) {
-	shell := os.Getenv("COMSPEC")
+	var shell string
+	if shell = os.Getenv("COMSPEC"); shell == "" {
+		shell = "cmd"
+	}
 	cmd := exec.Command(shell, "/c", line)
 	if dir != "" {
 		cmd.Dir = dir