[utils] Properly handle list values in update_url()

An actual list value in a query update could have been treated
as a list of values because of the key:list parse_qs format.

test/helper.py

@@ -142,7 +142,7 @@ def expect_value(self, got, expected, field):
         self.assertTrue(
             contains_str in got,
             'field %s (value: %r) should contain %r' % (field, got, contains_str))
-    elif isinstance(expected, compat_str) and re.match(r'^lambda \w+:', expected):
+    elif isinstance(expected, compat_str) and re.match(r'lambda \w+:', expected):
         fn = eval(expected)
         suite = expected.split(':', 1)[1].strip()
         self.assertTrue(

youtube_dl/utils.py

@@ -4257,7 +4257,7 @@ def update_url(url, **kwargs):
     query = kwargs.pop('query_update', None)
     if query:
         qs = compat_parse_qs(url.query)
-        qs.update(query)
+        qs.update((k, [v]) for k, v in query.items())
         kwargs['query'] = compat_urllib_parse_urlencode(qs, True)
         kwargs = compat_kwargs(kwargs)
     return compat_urllib_parse.urlunparse(url._replace(**kwargs))