chore(Python): Update ECDH extern, pin DafnyRuntimePython version (#819)

Author: lucasmcdonald3

AwsCryptographyPrimitives/runtimes/python/src/aws_cryptography_primitives/internaldafny/extern/ECDH.py

@@ -225,6 +225,15 @@ def GetPublicKey(dafny_eccAlgorithm, dafny_privateKey):
                         )
                     )
                 )
+        else:
+            return default__.CreateExternEccKeyGenFailure(
+                    _smithy_error_to_dafny_error(
+                        ValueError(
+                            "SM2 not supported."
+                        )
+                    )
+                )
+
 
     def ValidatePublicKey(dafny_eccAlgorithm, dafny_publicKey):
         public_key_bytes = bytes(dafny_publicKey)

StandardLibrary/runtimes/python/pyproject.toml

@@ -18,7 +18,7 @@ include = [
 python = "^3.11.0"
 pytz = "^2023.3.post1"
 # TODO: Longer-term, write something to pull this in from the project's project.properties file
-DafnyRuntimePython = "~4.8.0"
+DafnyRuntimePython = "4.8.1.post1"
 
 # Package testing