[i965][snb][bisected] piglit test 'implicitly-sized-array-length_frag' failure after enablement

Failure began with piglit=72700ee3 :

Author: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Date:   Mon Jul 19 14:58:19 2021 +0300

    tests: Add test for .length() method on implicitly-sized arrays
    
    Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
    Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
    Part-of: <https://gitlab.freedesktop.org/mesa/piglit/-/merge_requests/549>

stderr shows a shader compilation error:

Failed to compile fragment shader /tmp/build_root/m64/lib/piglit/tests/spec/arb_shader_storage_buffer_object/compiler/implicitly-sized-array-length.frag: 0:23(12): error: extension `GL_ARB_shader_storage_buffer_object' unsupported in fragment shader

Result posted here: https://mesa-ci.01.org/mesa_master/builds/27459/results/6999737440