list: Never lock the repository when listing lock files

There's no point in locking the repository just to list the currently
existing lock files. This won't work for an exclusively locked
repository and is also confusing to users.

cmd/restic/cmd_list.go

@@ -39,7 +39,7 @@ func runList(cmd *cobra.Command, opts GlobalOptions, args []string) error {
 		return err
 	}
 
-	if !opts.NoLock {
+	if !opts.NoLock && args[0] != "locks" {
 		lock, err := lockRepo(opts.ctx, repo)
 		defer unlockRepo(lock)
 		if err != nil {