Update web_base.py _fetch() method For SiteMapLoader (#6256)

A must-include for SiteMap Loader to avoid the SSL verification error.
Setting the 'verify' to False by ``` sitemap_loader.requests_kwargs =
{"verify": False}``` does not bypass the SSL verification in some
websites.

There are websites (https:// researchadmin.asu.edu/ sitemap.xml) where
setting "verify" to False as shown below would not work:
sitemap_loader.requests_kwargs = {"verify": False} 

We need this merge to tell the Session to use a connector with a
specific argument about SSL:
 \# For SiteMap SSL verification
if not self.request_kwargs['verify']:
    connector = aiohttp.TCPConnector(ssl=False)
else:
    connector = None
 
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Fixes #5483 

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@eyurtsev

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

langchain/document_loaders/web_base.py

@@ -100,7 +100,13 @@ class WebBaseLoader(BaseLoader):
     async def _fetch(
         self, url: str, retries: int = 3, cooldown: int = 2, backoff: float = 1.5
     ) -> str:
-        async with aiohttp.ClientSession() as session:
+        # For SiteMap SSL verification
+        if not self.requests_kwargs.get("verify", True):
+            connector = aiohttp.TCPConnector(ssl=False)
+        else:
+            connector = None
+
+        async with aiohttp.ClientSession(connector=connector) as session:
             for i in range(retries):
                 try:
                     async with session.get(