Update freshness.md (#5136)

clarified that freshness is supported in version 1.7.3 per @elyobo's pr
#4784.

confirmed in [internal
slack](https://dbt-labs.slack.com/archives/C067EUS2D7S/p1711102003658309)
as well.

website/docs/reference/resource-properties/freshness.md

@@ -48,7 +48,7 @@ If a source has a `freshness:` block, dbt will attempt to calculate freshness fo
 Currently, calculating freshness from warehouse metadata tables is supported on the following adapters:
 - [Snowflake](/reference/resource-configs/snowflake-configs)
 - [Redshift](/reference/resource-configs/redshift-configs)
-- [BigQuery](/reference/resource-configs/bigquery-configs)
+- [BigQuery](/reference/resource-configs/bigquery-configs) (Supported in [`dbt-bigquery`](https://github.com/dbt-labs/dbt-bigquery) version 1.7.3 or higher)
 
 Support is coming soon to the [Spark](/reference/resource-configs/spark-configs) adapter.