[#5218] Fix Configuration for max_staleness should be string with exp…

…licit format, instead of integer (#5220)

Resolves #5218 

## What are you changing in this pull request and why?
As stated in the issue description, while following the example code
snippets in the [Optimizing Materialized Views with dbt
](https://docs.getdbt.com/blog/announcing-materialized-views) page to
setup materialized views in BigQuery, I got a database error when I
defined `max_staleness=60` (as described in the blog).

When I instead changed that line of the `config` block to
`max_staleness='INTERVAL 60 MINUTE'`, the model successfully
materialized.

## Checklist

- [X] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
so my content adheres to these guidelines.
- [X]  Needs technical review

### Additional information

I tested with:
- `dbt-core`   v1.7.3
- `dbt-bigquery`  v1.7.1

website/blog/2023-08-01-announcing-materialized-views.md

@@ -150,7 +150,7 @@ config(
     on_configuration_change = 'apply',
     enable_refresh = True,
     refresh_interval_minutes = 30
-    max_staleness = 60,
+    max_staleness = 'INTERVAL 60 MINUTE'
 )
 }}
 ```