source-stripe-native: make created optional for Accounts

Sometimes, `account.updated` events do not have `created` in the
document, causing failures when we validate the document against its
model. Allowing a default value of `None` optional will avoid these
failures and reflect the API's actual response.

Note: We remove the `None` default value with a lambda to keep the
schema more inline with what actually happens: the `created` field is
either present as an `int` or it's not present at all.

source-stripe-native/source_stripe_native/models.py

@@ -151,6 +151,12 @@ class Accounts(BaseStripeObjectWithEvents):
         "account.updated": "u",
     }
 
+    # Accounts docs returned in account.updated events may not have a created field.
+    created: int = Field(
+        default=None,
+        # Don't schematize the default value.
+        json_schema_extra=lambda x: x.pop('default') # type: ignore
+    )
 
 # Could not verify Persons events are generated in test mode, but suspect
 # they are generated in Stripe's live mode.

source-stripe-native/tests/snapshots/snapshots__discover__stdout.json

@@ -59,8 +59,7 @@
       },
       "required": [
         "id",
-        "object",
-        "created"
+        "object"
       ],
       "title": "Accounts",
       "type": "object",