[3.13] pythongh-101100: Fix references in http.cookiejar docs (pythonGH-136238) (pythonGH-136317)

pythongh-101100: Fix references in `http.cookiejar` docs (pythonGH-136238)
(cherry picked from commit f0c7344)

Co-authored-by: Weilin Du <[email protected]>

Author: miss-islington

Doc/library/http.cookiejar.rst

@@ -570,7 +570,7 @@ Netscape protocol strictness switches:
 
    Don't allow setting cookies whose path doesn't path-match request URI.
 
-:attr:`strict_ns_domain` is a collection of flags.  Its value is constructed by
+:attr:`~DefaultCookiePolicy.strict_ns_domain` is a collection of flags.  Its value is constructed by
 or-ing together (for example, ``DomainStrictNoDots|DomainStrictNonDomain`` means
 both flags are set).