Rename …/data/test/…/DEMAND.csv.gz

[khaeru]

Avoid conflict with (lower-case) demand.csv.gz on case-insensitive file systems (e.g. macOS). I rename the file instead of deleting it because it's somewhat tedious to either (a) recreate or (b) go back into the Git history to later retrieve it, and there's no impact of keeping the renamed file around.

Closes #168.

How to review

Note that the CI checks all pass.

PR checklist

• [x] Continuous integration checks all ✅
• [x] ~Add or expand tests;~ coverage checks both ✅
• ~Add, expand, or update documentation.~ N/A
• ~Update doc/whatsnew.~

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.7%. Comparing base (7a35067) to head (a7d4497). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #181 +/- ## ===================================== Coverage 76.7% 76.7% ===================================== Files 112 112 Lines 7154 7154 ===================================== Hits 5494 5494 Misses 1660 1660 ```