update ssl verifying part to work with httpx 0.28.0 (#798)

As the new httpx 0.28.0 removes VerifyTypes, we should update to follow
their change
See [issue](#796)

---------

Co-authored-by: Eugene Yurtsev <[email protected]>

langserve/client.py

@@ -21,7 +21,7 @@
 from urllib.parse import urljoin
 
 import httpx
-from httpx._types import AuthTypes, CertTypes, CookieTypes, HeaderTypes, VerifyTypes
+from httpx._types import AuthTypes, CertTypes, CookieTypes, HeaderTypes
 from langchain_core.callbacks import (
     AsyncCallbackManagerForChainRun,
     CallbackManagerForChainRun,
@@ -49,6 +49,11 @@
 
 logger = logging.getLogger(__name__)
 
+import typing
+
+if typing.TYPE_CHECKING:  # We simply follow the way httpx do
+    import ssl
+
 
 def _is_json_serializable(obj: Any) -> bool:
     """Return True if the object is json serializable."""
@@ -281,7 +286,7 @@ def __init__(
         auth: Optional[AuthTypes] = None,
         headers: Optional[HeaderTypes] = None,
         cookies: Optional[CookieTypes] = None,
-        verify: VerifyTypes = True,
+        verify: ssl.SSLContext | str | bool = True,
         cert: Optional[CertTypes] = None,
         client_kwargs: Optional[Dict[str, Any]] = None,
         use_server_callback_events: bool = True,