fix(fw): pypy compatibility - replace bytes=self with just self. (#451)

pypy doesn't name this parameter for some reason.

src/ethereum_test_tools/vm/opcode.py

@@ -180,7 +180,7 @@ def int(self) -> int:
         """
         Returns the integer representation of the opcode.
         """
-        return int.from_bytes(bytes=self, byteorder="big")
+        return int.from_bytes(self, byteorder="big")
 
     def __str__(self) -> str:
         """