workflows: install gdk-pixbuf2-modules on Fedora
workflows: install gdk-pixbuf2-modules on Fedora

The BMP loader isn't installed by default.

Signed-off-by: Benjamin Gilbert <55d1d0083477f6dd5757d8929dd3b9e09d80bd84@cs.cmu.edu>

openslide/openslide,openslide/openslide,openslide/openslide,openslide/openslide