fix: stringifies date in DateTime field for useAsTitle (#1674)

Author: jacobsfletch

src/admin/components/forms/field-types/DateTime/index.tsx

@@ -88,7 +88,9 @@ const DateTime: React.FC<Props> = (props) => {
           {...date}
           placeholder={getTranslation(placeholder, i18n)}
           readOnly={readOnly}
-          onChange={readOnly ? undefined : setValue}
+          onChange={(incomingDate) => {
+            if (!readOnly) setValue(incomingDate.toISOString());
+          }}
           value={value as Date}
         />
       </div>

test/fields/collections/Date/index.ts

@@ -5,7 +5,7 @@ export const defaultText = 'default-text';
 const DateFields: CollectionConfig = {
   slug: 'date-fields',
   admin: {
-    useAsTitle: 'date',
+    useAsTitle: 'default',
   },
   fields: [
     {