nir/lower_tex: skip lower_tex_packing for the texture samples query

nir/lower_tex: skip lower_tex_packing for the texture samples query

Similar to other skips for texture queries that don't actually sample
the texture and which results are not packed.

We can't use nir_tex_instr_is_query() here to skip the lowering for all
queries since that causes regressions in Piglit. Apparently, we do want
to lower some of the query results. In particularly, the LOD query.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6169>