aws[patch]: fix initialization of BedrockLLM without client (#204)

`BedrockLLM.validate_environment` shadows its parent
`BedrockBase.validate_environment`, so the latter appears not to run.

Resolves #196

libs/aws/langchain_aws/llms/bedrock.py

@@ -1020,7 +1020,7 @@ class BedrockLLM(LLM, BedrockBase):
     """
 
     @model_validator(mode="after")
-    def validate_environment(self) -> Self:
+    def validate_environment_llm(self) -> Self:
         model_id = self.model_id
         if model_id.startswith("anthropic.claude-3"):
             raise ValueError(

libs/aws/tests/integration_tests/llms/test_bedrock.py

@@ -0,0 +1,8 @@
+from langchain_aws import BedrockLLM
+
+
+def test_bedrock_llm() -> None:
+    llm = BedrockLLM(model_id="anthropic.claude-v2:1")
+    response = llm.invoke("Hello")
+    assert isinstance(response, str)
+    assert len(response) > 0