tests/api: Adjust "client" fixture
tests/api: Adjust "client" fixture

Allow simple Flask apps too

shadowoneau/skylines,Turbo87/skylines,Turbo87/skylines,Harry-R/skylines,Harry-R/skylines,kerel-fs/skylines,kerel-fs/skylines,skylines-project/skylines,skylines-project/skylines,TobiasLohner/SkyLines,snip/skylines,skylines-project/skylines,snip/skylines,RBE-Avionik/skylines,RBE-Avionik/skylines,kerel-fs/skylines,skylines-project/skylines,shadowoneau/skylines,TobiasLohner/SkyLines,shadowoneau/skylines,RBE-Avionik/skylines,Turbo87/skylines,Turbo87/skylines,RBE-Avionik/skylines,Harry-R/skylines,TobiasLohner/SkyLines,snip/skylines,Harry-R/skylines,shadowoneau/skylines