community[patch]: fix instantiation for Slack tools (#28990)

Believe the current implementation raises PydanticUserError following
[this](https://github.com/pydantic/pydantic/releases/tag/v2.10.1)
Pydantic release.

Resolves #28989

Author: ccurme

libs/community/langchain_community/agent_toolkits/slack/toolkit.py

@@ -13,7 +13,14 @@
 from langchain_community.tools.slack.utils import login
 
 if TYPE_CHECKING:
+    # This is for linting and IDE typehints
     from slack_sdk import WebClient
+else:
+    try:
+        # We do this so pydantic can resolve the types when instantiating
+        from slack_sdk import WebClient
+    except ImportError:
+        pass
 
 
 class SlackToolkit(BaseToolkit):

libs/community/langchain_community/tools/slack/base.py

@@ -10,7 +10,14 @@
 from langchain_community.tools.slack.utils import login
 
 if TYPE_CHECKING:
+    # This is for linting and IDE typehints
     from slack_sdk import WebClient
+else:
+    try:
+        # We do this so pydantic can resolve the types when instantiating
+        from slack_sdk import WebClient
+    except ImportError:
+        pass
 
 
 class SlackBaseTool(BaseTool):  # type: ignore[override]