Fix: crn_version should be optional and given

Author: 1yam

src/aleph/sdk/client/services/crn.py

@@ -97,7 +97,7 @@ def find_gpu_on_network(self):
 
     def filter_crn(
         self,
-        crn_version: str = None,
+        crn_version: Optional[str] = None,
         ipv6: bool = False,
         stream_address: bool = False,
         confidential: bool = False,