Fix right type on create_session

[philogicae]

Fix for types and tests

[github-actions]

"summary": "The PR involves a significant change to the method signature and the way parameters are passed to the create_session method. This could potentially affect the behavior of the system and may introduce bugs if not handled correctly. The renaming of variables and the addition of new parameters indicate a more complex change that requires a deeper understanding of the codebase and its interactions.",
"highlight": [
{
"line": "certificate_prefix",
"comment": "New parameter introduced to replace vm_id."
},
{
"line": "platform_certificate_path",
"comment": "New parameter introduced to replace certificate_path."
},
{
"line": "await vm_client.create_session(certificate_prefix, platform_certificate_path, policy)",
"comment": "Call to the create_session method now requires three parameters instead of two."
}
]
}