Fix seed boolean null handling #3876

Job	Run time
changes	8s
test-dbt-versions (1.4)	1m 35s
test-dbt-versions (1.3)	1m 37s
test-dbt-versions (1.6)	1m 42s
test-dbt-versions (1.9)	1m 39s
test-dbt-versions (1.7)	1m 17s
test-dbt-versions (1.10)	1m 44s
test-dbt-versions (1.5)	1m 34s
test-dbt-versions (1.8)	1m 36s
test-vscode	0s
test-vscode-e2e	0s
migration-test	1m 39s
cicd-tests-windows	11m 44s
style-and-cicd-tests (3.12)	3m 5s
style-and-cicd-tests (3.10)	3m 9s
style-and-cicd-tests (3.13)	3m 0s
engine-tests-docker (mssql)	1m 55s
style-and-cicd-tests (3.11)	2m 49s
engine-tests-docker (clickhouse)	2m 43s
engine-tests-docker (mysql)	1m 46s
engine-tests-docker (trino)	8m 34s
engine-tests-docker (starrocks)	3m 12s
engine-tests-docker (risingwave)	2m 31s
doc-tests	31s
engine-tests-docker (postgres)	2m 12s
engine-tests-docker (spark)	5m 11s
style-and-cicd-tests (3.9)	3m 38s
engine-tests-docker (duckdb)	1m 40s
ui-test	-1s
ui-style	-1s
engine-tests-cloud	-1s
	1h 12m 8s

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