typing: suppress a few attribute errors in url.py

These are newly detected by pytype 2022.03.21.  Not sure what is going on here-
`realhostport` and `headers` are added outside of the constructor, so that makes
sense.  But PyCharm also thinks the private methods don't exist, though when
clicking through the class hierarchy, it shows in the py3.9 source code.

mercurial/url.py

@@ -222,13 +222,16 def _generic_start_transaction(handler,
     h.headers = None
 
 
-def _generic_proxytunnel(self):
+def _generic_proxytunnel(self: "httpsconnection"):
+    headers = self.headers  # pytype: disable=attribute-error
     proxyheaders = {
-        pycompat.bytestr(x): pycompat.bytestr(self.headers[x])
-        for x in self.headers
+        pycompat.bytestr(x): pycompat.bytestr(headers[x])
+        for x in headers
         if x.lower().startswith('proxy-')
     }
-    self.send(b'CONNECT %s HTTP/1.0\r\n' % self.realhostport)
+    realhostport = self.realhostport  # pytype: disable=attribute-error
+    self.send(b'CONNECT %s HTTP/1.0\r\n' % realhostport)
+
     for header in proxyheaders.items():
         self.send(b'%s: %s\r\n' % header)
     self.send(b'\r\n')
@@ -237,10 +240,14 def _generic_proxytunnel(self):
     # httplib.HTTPConnection as there are no adequate places to
     # override functions to provide the needed functionality.
 
+    # pytype: disable=attribute-error
     res = self.response_class(self.sock, method=self._method)
+    # pytype: enable=attribute-error
 
     while True:
+        # pytype: disable=attribute-error
         version, status, reason = res._read_status()
+        # pytype: enable=attribute-error
         if status != httplib.CONTINUE:
             break
         # skip lines that are all whitespace
@@ -323,14 +330,15 if has_https:
             self.sock = socket.create_connection((self.host, self.port))
 
             host = self.host
-            if self.realhostport:  # use CONNECT proxy
+            realhostport = self.realhostport  # pytype: disable=attribute-error
+            if realhostport:  # use CONNECT proxy
                 _generic_proxytunnel(self)
-                host = self.realhostport.rsplit(b':', 1)[0]
+                host = realhostport.rsplit(b':', 1)[0]
             self.sock = sslutil.wrapsocket(
                 self.sock,
                 self.key_file,
                 self.cert_file,
-                ui=self.ui,
+                ui=self.ui,  # pytype: disable=attribute-error
                 serverhostname=host,
             )
             sslutil.validatesocket(self.sock)