Warp_dem tests failing after environment update between 10.21 and 04.22

[rhugonnet]

When starting this PR again, there was a couple of failures in tests that had nothing to do with terrain.py despite the tests passing 6 months ago.
I managed to solve most of them (e.g. deprecation warnings, etc), but there is still 2 tests that are failing which are directly related to the warp_dem function and I couldn't fully grasp the source. In the meantime I added a skip decorator, and I will open a related issue so that @erikmannerfelt can check this later.

Originally posted by @rhugonnet in #227 (comment)