bug#44455: [ARTWORK] website: Not enough context for translation of None

[Miguel Ángel Arruga Vivas]

The string "None" does not have enough context and can lead to wrong
translations, as the word or even the gender may differ for each one.
This change also will invalidate the current translation.

The code fragment where it is used is included as reported in other
thread:

"pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de> writes:
>> (define (patches->shtml patches)
>> "Return an SHTML representation of PATCHES.
>>
>>  PATCHES (list)
>>    A list of <link> objects as defined in (apps packages types)
>>    module.
>>
>>  RETURN (shtml)
>>    If the list of patches is empty, return the string 'None'.
>>    Otherwise, return a list of links to patches."
>> (if (null? patches)
>>     (G_ "None")
>>     […]
>
>> (define (supported-systems->shtml package)
>>   "Return a list of SHTML a links to SYSTEMS builds.
>> […]
>>     (if (null? systems)
>>         (G_ "None")
>>         […]