Restoring cross-database compatibility of example code (#5785)

[Preview](https://docs-getdbt-com-git-dbeatty10-patch-1-dbt-labs.vercel.app/docs/build/incremental-models#filtering-rows-on-an-incremental-run)

## What are you changing in this pull request and why?

The code change in #5326
was tested against a variety of dbt adapters. The update in
#5306 modified that code
example, and it appears to have database-specific cast syntax (`::`) as
well as a data type that means different things in different databases
(i.e., the `TIMESTAMP` data type has different semantics in BigQuery vs.
Snowflake).

So we should restore the code example in
#5326. If there is a
better example that has been tested across dbt adapters, then we can
consider making another update in the future.

## 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.

website/docs/docs/build/incremental-models.md

@@ -71,7 +71,7 @@ from {{ ref('app_data_events') }}
   -- this filter will only be applied on an incremental run
   -- (uses >= to include records whose timestamp occurred since the last run of this model)
   -- (If event_time is NULL or the table is truncated, the condition will always be true and load all records)
-where event_time >= (select coalesce(max(event_time),'1900-01-01'::TIMESTAMP) from {{ this }} )
+where event_time >= (select coalesce(max(event_time),'1900-01-01') from {{ this }} )
 
 {% endif %}
 ```