Fix failing tests for XLA generation in TF (#18298)

* Fix failing test_xla_generate_slow tests

* Fix failing speech-to-text xla_generate tests

tests/test_modeling_tf_common.py

@@ -1685,6 +1685,17 @@ class TFModelTesterMixin:
             config.do_sample = False
             config.num_beams = num_beams
             config.num_return_sequences = num_return_sequences
+
+            # fix config for models with additional sequence-length limiting settings
+            for var_name in ["max_position_embeddings", "max_target_positions"]:
+                if hasattr(config, var_name):
+                    try:
+                        setattr(config, var_name, max_length)
+                    except NotImplementedError:
+                        # xlnet will raise an exception when trying to set
+                        # max_position_embeddings.
+                        pass
+
             model = model_class(config)
 
             if model.supports_xla_generation:
@@ -1714,15 +1725,6 @@ class TFModelTesterMixin:
 
         Either the model supports XLA generation and passes the inner test, or it raises an appropriate exception
         """
-        # TODO (Joao): find the issues related to the following models. They are passing the fast test, but failing
-        # the slow one.
-        if any(
-            [
-                model in str(self).lower()
-                for model in ["tfbart", "tfblenderbot", "tfmarian", "tfmbart", "tfopt", "tfpegasus"]
-            ]
-        ):
-            return
         num_beams = 8
         num_return_sequences = 2
         max_length = 128