Update requirements.txt to support PrivateKeyType and
PublicKeyType which are available in cryptography library since
version 40.0.0 and prevent failing CI jobs in upcoming changes.
Signed-off-by: Rustam Ismayilov <rustam.ismayilov@arm.com>
Change-Id: I94b888d64c2f33ccb829912491e3b8c44b9cc2b2