Fix type annotation for QueryCheckerTool.llm (#3237)

Currently `langchain.tools.sql_database.tool.QueryCheckerTool` has a
field `llm` with type `BaseLLM`. This breaks initialization for some
LLMs. For example, trying to use it with GPT4:

```python
from langchain.sql_database import SQLDatabase
from langchain.chat_models import ChatOpenAI
from langchain.tools.sql_database.tool import QueryCheckerTool


db = SQLDatabase.from_uri("some_db_uri")
llm = ChatOpenAI(model_name="gpt-4")
tool = QueryCheckerTool(db=db, llm=llm)

# pydantic.error_wrappers.ValidationError: 1 validation error for QueryCheckerTool
# llm
#   Can't instantiate abstract class BaseLLM with abstract methods _agenerate, _generate, _llm_type (type=type_error)
```

Seems like much of the rest of the codebase has switched from `BaseLLM`
to `BaseLanguageModel`. This PR makes the change for QueryCheckerTool as
well

Co-authored-by: Zachary Jones <[email protected]>

langchain/tools/sql_database/tool.py

@@ -6,7 +6,7 @@
 from langchain.chains.llm import LLMChain
 from langchain.prompts import PromptTemplate
 from langchain.sql_database import SQLDatabase
-from langchain.llms.base import BaseLLM
+from langchain.schema import BaseLanguageModel
 from langchain.tools.base import BaseTool
 from langchain.tools.sql_database.prompt import QUERY_CHECKER
 
@@ -81,7 +81,7 @@ class QueryCheckerTool(BaseSQLDatabaseTool, BaseTool):
     Adapted from https://www.patterns.app/blog/2023/01/18/crunchbot-sql-analyst-gpt/"""
 
     template: str = QUERY_CHECKER
-    llm: BaseLLM
+    llm: BaseLanguageModel
     llm_chain: LLMChain = Field(init=False)
     name = "query_checker_sql_db"
     description = """