fix test-lena

- The test for `add_lena_stats` referred to a GIN file on my computer - not the best idea. I left comments with instructions what to do in the code of the test.
- The other two failing tests fail for specific columns only: ctc in one case, adult_word_count - in another. I wonder if this has something to with floating point arithmetic differences between my macbook and my Dell. I should try running on macbook. The arithmetic issue already came up recently but I don't remember the context, I should search through Slack messages with Elika. Most likely, it was about the VIHI sampling paper.