Pin ixmp4 version temporarily to enable CI success

[glatterf42]

As announced in #975, this PR is a temporary workaround for that issue which aims to get our CI passing again.
I hope to have more time toward the end of the week to figure out a proper solution to the underlying issue.

How to review

• Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• [ ] Add, expand, or update documentation. Just CI.
• [ ] Update release notes. Just CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 25.9%. Comparing base (8f55fcf) to head (81101fa).
⚠️ Report is 1 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (8f55fcf) and HEAD (81101fa). Click for more details.

HEAD has 92 uploads less than BASE

Flag	BASE (8f55fcf)	HEAD (81101fa)
	95	3

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #976      +/-   ##
========================================
- Coverage   96.2%   25.9%   -70.4%     
========================================
  Files         60      60              
  Lines       5132    5132              
========================================
- Hits        4940    1330    -3610     
- Misses       192    3802    +3610     

see 57 files with indirect coverage changes

[glatterf42]

With the workaround (which would need to be limited to only the relevant Python versions still), we now see errors of this sort:

ERROR message_ix/tests/tools/test_sankey.py::test_map_for_sankey[ixmp4] - ModuleNotFoundError: No module named 'ixmp4.data.backend.test'

Which is understandable given the ixmp PRs' contents: it adjusted ixmp to the new ixmp4 versions in more ways than one, so we'd need to pin ixmp to a specific commit, too. Or we wait a few days for me to come back and provide better adjustments.

[khaeru]

Prior to the upstream changes, ixmp[ixmp4] had these dependencies, including ixmp4 >= 0.10, < 0.11.

In order to get the same installed versions of ixmp4/behaviour as prior to iiasa/ixmp#593, the simplest and most direct thing the present PR can do is to enforce those exact same version bounds. So that would mean specifying "ixmp4 < 0.11".

Making any adjustments to message_ix (such as needed for ixmp4 v0.11.0 and later) should be out of scope here.

[glatterf42]

True, but that won't resolve the current errors. These arise because we install ixmp from its main branch, which includes changes such as an updated import location of SqliteTestBackend. This won't be affected by further restrictions on the ixmp4 version.

[glatterf42]

Superseded by #977.