Don't use autospec in mock_sheet
Don't use autospec in mock_sheet

1b5d844abd4da652ae9b3272a95c6440b7e1e1f0 fixed a typo, however only this
typo actually made mock_sheet work due to the intended
GenericResourceSheet spec not being used.

This now removes the autospec again -> FIXME - joka will have a look
sometime later.

xs2maverick/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,xs2maverick/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator,fhartwig/adhocracy3.mercator,liqd/adhocracy3.mercator,fhartwig/adhocracy3.mercator