util/cache_test: Fix disabled cache test using SHADER_CACHE_DISABLE_BY_DEFAULT

util/cache_test: Fix disabled cache test using SHADER_CACHE_DISABLE_BY_DEFAULT

Previous commit decoupled EGL_ANDROID_blob_cache from the disk cache
and haven't updated the SHADER_CACHE_DISABLE_BY_DEFAULT test-case that
is failing because now cache is always created even if disk cache is
disabled, such cache is NO-OP in this case. Fix the failing test.

Fixes: 39f26642 ("util: Decouple disk cache from EGL_ANDROID_blob_cache")
Reviewed-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24985>