Fix(redshift): add missing db_user parameter for IAM auth (#5687) #3969

Job	Run time
changes	6s
test-dbt-versions (1.3)	1m 41s
test-dbt-versions (1.4)	1m 29s
test-dbt-versions (1.5)	1m 30s
test-dbt-versions (1.8)	1m 40s
test-dbt-versions (1.10)	1m 47s
test-dbt-versions (1.6)	1m 33s
test-dbt-versions (1.9)	1m 41s
test-dbt-versions (1.7)	1m 43s
test-vscode	0s
test-vscode-e2e	0s
ui-test	1m 23s
doc-tests	30s
cicd-tests-windows	10m 46s
migration-test	1m 26s
style-and-cicd-tests (3.9)	23m 56s
style-and-cicd-tests (3.12)	25m 10s
style-and-cicd-tests (3.10)	22m 59s
style-and-cicd-tests (3.13)	19m 5s
engine-tests-docker (mysql)	1m 44s
engine-tests-docker (risingwave)	2m 56s
engine-tests-docker (trino)	8m 23s
style-and-cicd-tests (3.11)	25m 10s
engine-tests-docker (mssql)	2m 2s
engine-tests-docker (postgres)	3m 10s
engine-tests-docker (duckdb)	1m 36s
engine-tests-docker (spark)	5m 0s
engine-tests-docker (clickhouse)	3m 15s
engine-tests-docker (starrocks)	2m 31s
ui-style	0s
engine-tests-cloud (bigquery)	20m 14s
engine-tests-cloud (clickhouse-cloud)	12m 9s
engine-tests-cloud (snowflake)	12m 26s
engine-tests-cloud (athena)	22m 34s
engine-tests-cloud (databricks)	12m 44s
engine-tests-cloud (fabric)	5m 6s
engine-tests-cloud (redshift)	9m 26s
engine-tests-cloud (gcp-postgres)	3m 16s
	4h 32m 7s

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