add _supports_flex_attn = True for models that do support it (#35598)

* add `_supports_flex_attn = True`

* fix repo consistency

src/transformers/models/aria/modeling_aria.py

@@ -704,6 +704,7 @@ class AriaPreTrainedModel(PreTrainedModel):
     _skip_keys_device_placement = ["past_key_values"]
     _supports_flash_attn_2 = True
     _supports_sdpa = True
+    _supports_flex_attn = True
     _supports_cache_class = True
     _supports_quantized_cache = True
     _supports_static_cache = True