community[patch]: fix model initialization bug for deepinfra (#25727)

### Description
adds an init method to ChatDeepInfra to set the model_name attribute
accordings to the argument
### Issue
currently, the model_name specified by the user during initialization of
the ChatDeepInfra class is never set. Therefore, it always chooses the
default model (meta-llama/Llama-2-70b-chat-hf, however probably since
this is deprecated it always uses meta-llama/Llama-3-70b-Instruct). We
stumbled across this issue and fixed it as proposed in this pull
request. Feel free to change the fix according to your coding guidelines
and style, this is just a proposal and we want to draw attention to this
problem.
### Dependencies
no additional dependencies required

Feel free to contact me or @timo282 and @finitearth if you have any
questions.

---------

Co-authored-by: Bagatur <[email protected]>
Co-authored-by: Bagatur <[email protected]>

libs/community/langchain_community/chat_models/deepinfra.py

@@ -222,6 +222,11 @@ class ChatDeepInfra(BaseChatModel):
     streaming: bool = False
     max_retries: int = 1
 
+    class Config:
+        """Configuration for this pydantic object."""
+
+        allow_population_by_field_name = True
+
     @property
     def _default_params(self) -> Dict[str, Any]:
         """Get the default parameters for calling OpenAI API."""

libs/community/tests/unit_tests/chat_models/test_deepinfra.py

@@ -0,0 +1,11 @@
+from langchain_community.chat_models import ChatDeepInfra
+
+
+def test_deepinfra_model_name_param() -> None:
+    llm = ChatDeepInfra(model_name="foo")  # type: ignore[call-arg]
+    assert llm.model_name == "foo"
+
+
+def test_deepinfra_model_param() -> None:
+    llm = ChatDeepInfra(model="foo")
+    assert llm.model_name == "foo"