Fix(redshift): add missing db_user parameter for IAM auth #3652

Job	Run time
changes	6s
test-dbt-versions (1.4)	1m 36s
test-dbt-versions (1.7)	1m 39s
test-dbt-versions (1.6)	1m 35s
test-dbt-versions (1.3)	1m 30s
test-dbt-versions (1.9)	1m 46s
test-dbt-versions (1.8)	1m 46s
test-dbt-versions (1.10)	1m 41s
test-dbt-versions (1.5)	1m 39s
test-vscode	0s
test-vscode-e2e	-1s
doc-tests	36s
style-and-cicd-tests (3.12)	22m 18s
style-and-cicd-tests (3.10)	23m 22s
style-and-cicd-tests (3.9)	23m 27s
cicd-tests-windows	10m 39s
migration-test	1m 26s
style-and-cicd-tests (3.11)	23m 6s
style-and-cicd-tests (3.13)	22m 16s
engine-tests-docker (postgres)	2m 32s
engine-tests-docker (trino)	8m 23s
engine-tests-docker (duckdb)	1m 35s
engine-tests-docker (risingwave)	2m 35s
engine-tests-docker (mysql)	1m 44s
engine-tests-docker (spark)	5m 43s
engine-tests-docker (mssql)	1m 45s
engine-tests-docker (clickhouse)	2m 42s
ui-test	0s
ui-style	0s
engine-tests-cloud	0s
	2h 47m 26s

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