fix: Set DatabricksConnectionConfig to only use a shared_connection with U2M OAuth #3903

Job	Run time
changes	6s
test-dbt-versions (1.8)	1m 41s
test-dbt-versions (1.5)	1m 35s
test-dbt-versions (1.9)	1m 45s
test-dbt-versions (1.4)	1m 23s
test-dbt-versions (1.7)	1m 49s
test-dbt-versions (1.6)	1m 37s
test-dbt-versions (1.3)	1m 47s
test-dbt-versions (1.10)	1m 41s
test-vscode	0s
test-vscode-e2e	0s
doc-tests	38s
migration-test	1m 33s
cicd-tests-windows	10m 33s
style-and-cicd-tests (3.12)	24m 19s
engine-tests-docker (duckdb)	1m 30s
engine-tests-docker (mysql)	1m 40s
style-and-cicd-tests (3.10)	16m 31s
style-and-cicd-tests (3.9)	24m 33s
style-and-cicd-tests (3.11)	23m 48s
engine-tests-docker (postgres)	2m 12s
engine-tests-docker (spark)	5m 37s
engine-tests-docker (clickhouse)	2m 59s
engine-tests-docker (mssql)	1m 55s
engine-tests-docker (trino)	8m 6s
engine-tests-docker (risingwave)	2m 45s
engine-tests-docker (starrocks)	2m 38s
style-and-cicd-tests (3.13)	22m 4s
ui-test	0s
ui-style	0s
engine-tests-cloud	0s
	2h 46m 45s

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