[fix] engines: base URL can be a list or a string, but its not None!

The code injection and monkey patching examine the names in the module of the
engine; if a variable there starts without an underscore and has the value None,
then this variable needs to be configured. This outdated concept does not fit
engines that may have multiple URLs. At least not as long as the value of the
base URL (list) is None.

The default is now an empty list instead of None

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/engines/invidious.py

@@ -31,7 +31,7 @@ paging = True
 time_range_support = True
 
 # base_url can be overwritten by a list of URLs in the settings.yml
-base_url: list | str = []
+base_url: list[str] | str = []
 
 
 def init(_):