fix: Add external_id to mock repos in SCM onboarding acceptance tests

The new externalId field in OrganizationIntegrationReposEndpoint
requires external_id in the repository data. The acceptance test
mocks were missing this field, causing KeyError → 500 errors.

Author: wedamija

tests/acceptance/test_scm_onboarding.py

@@ -52,6 +52,7 @@ def test_scm_onboarding_happy_path(self) -> None:
                 "name": "sentry",
                 "identifier": "getsentry/sentry",
                 "default_branch": "master",
+                "external_id": "12345",
             },
         ]
 
@@ -162,6 +163,7 @@ def test_scm_onboarding_with_integration_install(self) -> None:
                 "name": "sentry",
                 "identifier": "getsentry/sentry",
                 "default_branch": "master",
+                "external_id": "12345",
             },
         ]
 
@@ -273,6 +275,7 @@ def test_scm_onboarding_detection_error_falls_back_to_manual_picker(self) -> Non
                 "name": "sentry",
                 "identifier": "getsentry/sentry",
                 "default_branch": "master",
+                "external_id": "12345",
             },
         ]