Fix `FlaxMarianMTModel` return block. (#14873)

* Fixes in marian doc

* Another time

* Add return block in FlaxMarianMTModel

src/transformers/models/marian/modeling_flax_marian.py

@@ -38,7 +38,13 @@ from ...modeling_flax_outputs import (
     FlaxSeq2SeqLMOutput,
     FlaxSeq2SeqModelOutput,
 )
-from ...modeling_flax_utils import ACT2FN, FlaxPreTrainedModel, append_call_sample_docstring, overwrite_call_docstring
+from ...modeling_flax_utils import (
+    ACT2FN,
+    FlaxPreTrainedModel,
+    append_call_sample_docstring,
+    append_replace_return_docstrings,
+    overwrite_call_docstring,
+)
 from ...utils import logging
 from .configuration_marian import MarianConfig
 
@@ -1493,3 +1499,4 @@ overwrite_call_docstring(
     FlaxMarianMTModel,
     MARIAN_INPUTS_DOCSTRING + FLAX_MARIAN_MT_DOCSTRING,
 )
+append_replace_return_docstrings(FlaxMarianMTModel, output_type=FlaxSeq2SeqLMOutput, config_class=_CONFIG_FOR_DOC)