Fix: create_external_models misclassifies cross-repo models as external #3602

Job	Run time
changes	6s
test-dbt-versions (1.4)	1m 33s
test-dbt-versions (1.5)	1m 38s
test-dbt-versions (1.6)	1m 40s
test-dbt-versions (1.10)	1m 44s
test-dbt-versions (1.8)	1m 38s
test-dbt-versions (1.7)	2m 2s
test-dbt-versions (1.9)	1m 49s
test-dbt-versions (1.3)	1m 39s
test-vscode-e2e	-1s
test-vscode	-1s
doc-tests	36s
cicd-tests-windows	11m 47s
migration-test	1m 33s
style-and-cicd-tests (3.10)	24m 27s
style-and-cicd-tests (3.9)	22m 37s
style-and-cicd-tests (3.13)	23m 58s
style-and-cicd-tests (3.12)	24m 8s
engine-tests-docker (trino)	8m 19s
engine-tests-docker (postgres)	2m 20s
style-and-cicd-tests (3.11)	23m 33s
engine-tests-docker (clickhouse)	2m 59s
engine-tests-docker (mssql)	2m 2s
engine-tests-docker (duckdb)	1m 40s
engine-tests-docker (mysql)	1m 43s
engine-tests-docker (spark)	5m 31s
engine-tests-docker (risingwave)	2m 40s
ui-style	0s
ui-test	0s
engine-tests-cloud	0s
	2h 53m 40s

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