gpodder: update from 3.8.0 to 3.8.3

Hi,

I updated the gpodder package. I also moved the entries from `propagatedBuildInputs` to `pythonPath`, which is more appropriate for this package. The `gpodderHome` and `gpodderDownload` variables are removed, because they are useless. The variables should be set as normal environment variables.

Best,
Sven