tests: add import for python-cryptography >= 43.0.0

write_pkcs12_container method raises following error message with
python-cryptography-43.0.0:

  Error: module 'cryptography.hazmat.primitives.serialization' has no attribute 'pkcs12'

Explicit import of the pkcs12 module resolves the issue.

tests/make_certificates.py

@@ -10,6 +10,8 @@
 from cryptography.hazmat.primitives import serialization
 from cryptography.hazmat.primitives.asymmetric import rsa
 
+import cryptography.hazmat.primitives.serialization.pkcs12
+
 RESULT_PATH = os.getcwd()
 CERTS_PATH = os.path.join(RESULT_PATH, "./Testing/certs/")