Switch to using URL.host_port_subcomponent in yarl for the client…

… host header (#9575)

aiohttp/client_reqrep.py

@@ -362,30 +362,11 @@ def update_headers(self, headers: Optional[LooseHeaders]) -> None:
         self.headers: CIMultiDict[str] = CIMultiDict()
 
         # Build the host header
-        host = self.url.host_subcomponent
+        host = self.url.host_port_subcomponent
 
-        # host_subcomponent is None when the URL is a relative URL.
+        # host_port_subcomponent is None when the URL is a relative URL.
         # but we know we do not have a relative URL here.
         assert host is not None
-
-        if host[-1] == ".":
-            # Remove all trailing dots from the netloc as while
-            # they are valid FQDNs in DNS, TLS validation fails.
-            # See https://github.com/aio-libs/aiohttp/issues/3636.
-            # To avoid string manipulation we only call rstrip if
-            # the last character is a dot.
-            host = host.rstrip(".")
-
-        # If explicit port is not None, it means that the port was
-        # explicitly specified in the URL. In this case we check
-        # if its not the default port for the scheme and add it to
-        # the host header. We check explicit_port first because
-        # yarl caches explicit_port and its likely to already be
-        # in the cache and non-default port URLs are far less common.
-        explicit_port = self.url.explicit_port
-        if explicit_port is not None and not self.url.is_default_port():
-            host = f"{host}:{explicit_port}"
-
         self.headers[hdrs.HOST] = host
 
         if not headers: