Update model-contracts.md for supported models (#4336)

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Update to show that incremental models with on_schema_change: fail are
actually supported (only on_schema_change: append_new_columns is
mentioned but this was changed here
dbt-labs/dbt-core#8006)

Reformatted the list to make it clearer what is and isn't supported.

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website/docs/docs/collaborate/govern/model-contracts.md

@@ -28,10 +28,18 @@ While this is ideal for quick and iterative development, for some models, consta
 ## Where are contracts supported?
 
 At present, model contracts are supported for:
-- SQL models. Contracts are not yet supported for Python models.
-- Models materialized as `table`, `view`, and `incremental` (with `on_schema_change: append_new_columns`). Views offer limited support for column names and data types, but not `constraints`. Contracts are not supported for `ephemeral`-materialized models.
+- SQL models. 
+- Models materialized as one of the following:
+    - `table`
+    - `view` — Views offer limited support for column names and data types, but not `constraints`.
+    - `incremental` — with `on_schema_change: append_new_columns` or `on_schema_change: fail`.  
 - Certain data platforms, but the supported and enforced `constraints` vary by platform.
 
+Model contracts are _not_ supported for:
+- Python models.
+- `ephemeral`-materialized SQL models.
+
+
 ## How to define a contract
 
 Let's say you have a model with a query like: