Fix: mypy failed because of invalid type value

Mypy failed because a value should be convert to Gigabytes before using the
function gigabyte_to_megabyte.
Solution: Convert the number to Gigabytes before using the function

aleph_message/models/execution/volume.py

@@ -32,7 +32,7 @@ def is_read_only(self):
 
 class EphemeralVolumeSize(ConstrainedInt):
     gt = 0
-    le = gigabyte_to_mebibyte(10)  # Limit to 10 GB
+    le = gigabyte_to_mebibyte(Gigabytes(10))  # Limit to 10 GB
     strict = True