Test fence register shortage at (i915) driver

Test that glBlitFramebufferEXT with GL_NEAREST does not use too many fence registers at the blit, causing loss of current batchbuffer and missing data on the screen or causing an abort at an assert, if compiled with debug.

Verifies MR:
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26769

Signed-off-by: GKraats vd.kraats@hccnet.nl