fix: fix type for Header.schema fixed field

src/oas.md

@@ -2622,7 +2622,7 @@ The `example` and `examples` fields are mutually exclusive, and if either is pre
 | ---- | :----: | ---- |
 | <a name="header-style"></a>style | `string` | Describes how the header value will be serialized. The default (and only legal value for headers) is `"simple"`. |
 | <a name="header-explode"></a>explode | `boolean` | When this is true, header values of type `array` or `object` generate a single header whose value is a comma-separated list of the array items or key-value pairs of the map, see [Style Examples](#style-examples). For other data types this field has no effect. The default value is `false`. |
-| <a name="header-schema"></a>schema | [Schema Object](#schema-object) \| [Reference Object](#reference-object) | The schema defining the type used for the header. |
+| <a name="header-schema"></a>schema | [Schema Object](#schema-object) | The schema defining the type used for the header. |
 | <a name="header-example"></a>example | Any | Example of the header's potential value; see [Working With Examples](#working-with-examples). |
 | <a name="header-examples"></a>examples | Map[ `string`, [Example Object](#example-object) \| [Reference Object](#reference-object)] | Examples of the header's potential value; see [Working With Examples](#working-with-examples). |