glsl-fs-discard-mrt: New test for bug 75207
v2: Fold in winsys fbo binding bugfix that was reviewed on the ML, though the original test never was.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75207
v2: Fold in winsys fbo binding bugfix that was reviewed on the ML, though the original test never was.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75207