cmake / test: fix typo in wrong env option error

Change-Id: I08ecc40999ae3326bf0939a8b7d99bd5c3b0ef05
Reviewed-on: http://gerrit.aldebaran.lan/40567
Reviewed-by: vbarbaresi <vbarbaresi@aldebaran-robotics.com>
Reviewed-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>
Tested-by: vpaleologue <vpaleologue@aldebaran-robotics.com>