Fix: create_external_models misclassifies cross-repo models as external #3598

Job	Run time
changes	9s
test-vscode	0s
test-dbt-versions (1.3)	1m 40s
test-dbt-versions (1.10)	1m 42s
test-dbt-versions (1.6)	1m 47s
test-dbt-versions (1.8)	1m 35s
test-dbt-versions (1.9)	1m 47s
test-vscode-e2e	0s
test-dbt-versions (1.4)	1m 52s
test-dbt-versions (1.5)	1m 35s
test-dbt-versions (1.7)	1m 39s
cicd-tests-windows	11m 36s
doc-tests	35s
style-and-cicd-tests (3.11)	2m 51s
style-and-cicd-tests (3.9)	2m 47s
engine-tests-docker (mysql)	2m 6s
style-and-cicd-tests (3.13)	3m 28s
engine-tests-docker (trino)	8m 19s
engine-tests-docker (clickhouse)	5m 7s
engine-tests-docker (duckdb)	1m 46s
engine-tests-docker (postgres)	2m 20s
style-and-cicd-tests (3.12)	3m 51s
engine-tests-docker (mssql)	1m 52s
style-and-cicd-tests (3.10)	2m 58s
engine-tests-docker (risingwave)	5m 27s
engine-tests-docker (spark)	5m 20s
ui-style	-1s
ui-test	-1s
migration-test	1m 32s
engine-tests-cloud	0s
	1h 15m 39s

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