Fix model card date for add_dates.py check

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: artemspector

docs/source/en/model_doc/granite4_vision.md

@@ -13,7 +13,7 @@ specific language governing permissions and limitations under the License.
 rendered properly in your Markdown viewer.
 
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-*This model was released on 2026-03-27 and added to Hugging Face Transformers on 2026-04-23.*
+*This model was released on 2026-03-27 and added to Hugging Face Transformers on 2026-04-28.*
 
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