Work around pyam logging config

[khaeru]

This PR exists to debug https://github.com/iiasa/message-ix-models/issues/173#issuecomment-2063258654. If/when ixmp4 is updated to address its behaviour of removing the message-ix-models log handlers, the branch can be used to confirm a fix before it is merged there.

We may discard this branch without merging if no change is ultimately required in message-ix-models; or repurpose it to implement and confirm some kind of wrapper that works around the behaviour of ixmp4.

How to review

Ensure 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 (0108a04) to head (75dbfc0). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #175 +/- ## ======================================= - Coverage 76.8% 76.7% -0.1% ======================================= Files 112 112 Lines 7154 7154 ======================================= - Hits 5495 5494 -1 - Misses 1659 1660 +1 ``` [see 1 file with indirect coverage changes](https://app.codecov.io/gh/iiasa/message-ix-models/pull/175/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iiasa)

[khaeru]

@glatterf42 I'd suggested to squash-and-merge once the changes are reduced the one in the above comment. No need to spend time tidying up the branch history.

[khaeru]

Not sure what's up with the coverage report

It's because I added -k that reduced the set of tests run.