tests: don't set caps on unwritable buffers
tests: don't set caps on unwritable buffers

Take the ref after setting the caps on a buffer because else the buffer is
techinically not writable.

lovebug356/gstreamer,shelsonjava/gstreamer,magcius/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,collects/gstreamer,ahmedammar/platform_external_gst_gstreamer,mparis/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,lubosz/gstreamer,ylatuya/gstreamer,cablelabs/gstreamer,ahmedammar/platform_external_gst_gstreamer,ahmedammar/platform_external_gst_gstreamer,Distrotech/gstreamer,magcius/gstreamer,centricular/gstreamer,krichter722/gstreamer,mrchapp/gstreamer,magcius/gstreamer,shelsonjava/gstreamer,cfoch/gstreamer,surround-io/gstreamer,drothlis/gstreamer,cfoch/gstreamer,collects/gstreamer,surround-io/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,cablelabs/gstreamer,krichter722/gstreamer,Distrotech/gstreamer,mparis/gstreamer,collects/gstreamer,jpakkane/gstreamer,drothlis/gstreamer,drothlis/gstreamer,lubosz/gstreamer,mparis/gstreamer,jpakkane/gstreamer,lubosz/gstreamer,collects/gstreamer,jpxiong/gstreamer,drothlis/gstreamer,cablelabs/gstreamer,ahmedammar/platform_external_gst_gstreamer,cablelabs/gstreamer,drothlis/gstreamer,Lachann/gstreamer,lovebug356/gstreamer,mrchapp/gstreamer,Lachann/gstreamer,ensonic/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,surround-io/gstreamer,justinjoy/gstreamer,centricular/gstreamer,lovebug356/gstreamer,ensonic/gstreamer,ensonic/gstreamer,StreamUtils/gstreamer,justinjoy/gstreamer,ylatuya/gstreamer,jpakkane/gstreamer,krieger-od/gstreamer,mrchapp/gstreamer,jpakkane/gstreamer,cfoch/gstreamer,krieger-od/gstreamer,magcius/gstreamer,Lachann/gstreamer,Lachann/gstreamer,mparis/gstreamer,centricular/gstreamer,krichter722/gstreamer,cfoch/gstreamer,Distrotech/gstreamer,mrchapp/gstreamer,ylatuya/gstreamer,StreamUtils/gstreamer,krieger-od/gstreamer,ylatuya/gstreamer,lubosz/gstreamer,justinjoy/gstreamer,lubosz/gstreamer,lovebug356/gstreamer,StreamUtils/gstreamer,Distrotech/gstreamer,mparis/gstreamer,justinjoy/gstreamer,ensonic/gstreamer,magcius/gstreamer,mrchapp/gstreamer,collects/gstreamer,shelsonjava/gstreamer,Distrotech/gstreamer,cfoch/gstreamer,surround-io/gstreamer,ylatuya/gstreamer,justinjoy/gstreamer,lovebug356/gstreamer,Lachann/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,ahmedammar/platform_external_gst_gstreamer,surround-io/gstreamer,jpakkane/gstreamer,krieger-od/gstreamer,ensonic/gstreamer,krieger-od/gstreamer,cablelabs/gstreamer