Make test more specific to avoid error

[glatterf42]

The recent dask update has brought to light an issue with one of our tests. test_macro.py:test_config wants to test, among others, that a missing column is causing a related error message. However, the test deletes three columns from the config and with the recent update, a different column from the expected one is picked up for the error message. This PR changes the test to delete only the one column from the config that we expect in the error message.

How to review

• Read the diff and 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.~ Just tests
• ~[ ] Update release notes.~ Just tests

[codecov[bot]]

Codecov Report

Merging #767 (19391bf) into main (6b4f630) will not change coverage. The diff coverage is 100.0%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #767 +/- ## ===================================== Coverage 95.2% 95.2% ===================================== Files 46 46 Lines 4312 4312 ===================================== Hits 4107 4107 Misses 205 205 ``` | [Files](https://app.codecov.io/gh/iiasa/message_ix/pull/767?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iiasa) | Coverage Δ | | |---|---|---| | [message\_ix/tests/test\_macro.py](https://app.codecov.io/gh/iiasa/message_ix/pull/767?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iiasa#diff-bWVzc2FnZV9peC90ZXN0cy90ZXN0X21hY3JvLnB5) | `100.0% <100.0%> (ø)` | |