Skip FRAMEBUFFER_UNSUPPORTED subtests on DSA textures_buffer

Skip FRAMEBUFFER_UNSUPPORTED subtests on DSA textures_buffer

From OpenGL 4.5 spec, section 9.4.2 "Whole Framebuffer Completeness":

   "Although the GL defines a wide variety of internal formats for
    framebuffer-attachable images, such as texture images and
    renderbuffer images, some implementations may not support
    rendering to particular combinations of internal formats. If the
    combination of formats of the images attached to a framebuffer
    object are not supported by the implementation, then the
    framebuffer is not complete under the clause labeled
    FRAMEBUFFER_UNSUPPORTED .

    Implementations are required to support certain combinations of
    framebuffer internal formats as described under “Required
    Framebuffer Formats” in sec- tion 9.4.3."

That means that if the combination being tested returns
FRAMEBUFFER_UNSUPPORTED, it is still allowed by OpenGL spec. For those
cases, the test should skip instead of fail.

Affects:
GL45-CTS.direct_state_access.textures_buffer

Components: OpenGL

VK-GL-CTS: 201

Change-Id: Ia272a975e8417837637cd47b621b91306d1aa567