tests: Use a pixel shader that consumes SV_Position in test_query_pipeline_statistics().
Some drivers (AMD Radeon RX 6700 XT, with radeonsi from Mesa 22.2.0-rc3) emit less than one invocation per pixel, presumably because they detect that the shader control flow is uniform for all pixels. Having the control flow depend on SV_Position avoids this test failure.
Cf. 34bd0dd0704c613abef8a9aa3ba2a2507ed02843 in wine.