You don't need the extras-testing repository.
It was part of the QA process but seen as zero packages get QA'ed any more it's not worth using.
Extras have passed community QA and extra-devel use at your own risk they haven't been tested or past QA checks.
GPG isn't an error it's a warning and not fixable
It's not advised to use apt on Maemo it was only ever intended to install packages via HAM.
Hardly any browser works well any more, reports are people have best result with easy-debian for browsing