ci: Uprev piglit to af1785f31

Brings in these changes:

dad078717 occlusion_query_conform: convert to pilgit subtests
b52c1c761 glsl-1.30: test nested preprocessor concat
6c4da153b texture-storage: Fix subtest result handling of skips.
4343f19db fbo-integer: Remove the invalid DrawPixels test.
e3842f2fe arb_dsa: exclude stencil8 textures from test sets.
ce8649be7 spec/ext_external_objects: Fix build on Debian systems
4e553838f glsl: add basic tests for desktop GLSL invariant qualifier linking
7e61e5199 Tests for variable in and out of loop scope
f855ad1c8 fbo-mrt-alphatest: Only require GLSL 1.20
9be2fe999 glx: add glx-multi-display-single-pbuffer test
bfe290725 glx: add glx-swap-pbuffer test
efa64335e framework: Fix build on Windows when using waffle```

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>