Swap macos-13 → -15-intel runners in CI

[khaeru]

Per actions/runner-images#13046:

• The macos-13 runner images are deprecated and will become unavailable.
• A new image macos-15-intel is available.

The reason we were still using macos-13 is that message-ix-models still supports ixmp/message_ix v3.8 and v3.9. These versions neither (a) bundled binary GAMS libraries for arm64 (such as needed on the macos-latest runner) nor (b) included iiasa/ixmp#532 that adapted JDBCBackend to locate these libraries within the local GAMS installation. Thus, tests for these versions can't be run on arm64 systems (like macos-latest) and had to run on macos-13, which is x86-64. The new -intel image makes it possible to run the tests.

How to review

• Read the diff/
• 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. N/A; CI changes only.
• Update doc/whatsnew ditto.
• (After approval, before merge) Rebase to drop the TEMPORARY commit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.8%. Comparing base (ccb9393) to head (1b6fb10).

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #453     +/-   ##
=======================================
- Coverage   75.5%   74.8%   -0.7%     
=======================================
  Files        277     277             
  Lines      22674   22663     -11     
=======================================
- Hits       17136   16974    -162     
- Misses      5538    5689    +151     

Files with missing lines	Coverage Δ
message_ix_models/model/transport/testing.py	100.0% <ø> (ø)
message_ix_models/testing/__init__.py	80.0% <ø> (-14.0%)	⬇️
...sage_ix_models/tests/model/transport/test_build.py	83.7% <ø> (-0.2%)	⬇️
...age_ix_models/tests/model/transport/test_demand.py	97.9% <ø> (-0.1%)	⬇️
...age_ix_models/tests/model/transport/test_report.py	94.3% <ø> (-0.2%)	⬇️
message_ix_models/tests/project/test_navigate.py	92.6% <ø> (-0.2%)	⬇️
message_ix_models/tests/test_workflow.py	100.0% <ø> (ø)

... and 7 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[khaeru]

The job macos-15-latest-py3.14-upstream-v3.9.0 failed with:

Traceback (most recent call last):
  File "/Users/runner/work/message-ix-models/message-ix-models/.venv/bin/mix-models", line 4, in <module>
    from message_ix_models.cli import main
  File "/Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/message_ix_models/__init__.py", line 7, in <module>
    from message_ix_models.util._logging import setup as setup_logging
  File "/Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/message_ix_models/util/__init__.py", line 10, in <module>
    import message_ix
  File "/Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/message_ix/__init__.py", line 10, in <module>
    from ixmp import ModelError, config
  File "/Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/ixmp/__init__.py", line 7, in <module>
    from ixmp.backend.jdbc import JDBCBackend
  File "/Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/ixmp/backend/jdbc.py", line 15, in <module>
    import jpype
  File "/Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/jpype/__init__.py", line 18, in <module>
    import _jpype
ImportError: dlopen(/Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/_jpype.cpython-314-darwin.so, 0x0002): Library not loaded: /Users/runner/work/_temp/uv-python-dir/cpython-3.14.0-macos-x86_64-none/lib/libpython3.14.dylib
  Referenced from: <815392C5-0DE0-3774-9C28-802AB6299BDA> /Users/runner/work/message-ix-models/message-ix-models/.venv/lib/python3.14/site-packages/_jpype.cpython-314-darwin.so
  Reason: tried: '/Users/runner/work/_temp/uv-python-dir/cpython-3.14.0-macos-x86_64-none/lib/libpython3.14.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS/Users/runner/work/_temp/uv-python-dir/cpython-3.14.0-macos-x86_64-none/lib/libpython3.14.dylib' (no such file), '/Users/runner/work/_temp/uv-python-dir/cpython-3.14.0-macos-x86_64-none/lib/libpython3.14.dylib' (no such file)

I think this is because there are no pre-built binary wheels for JPype1 on Python 3.14/x86_64; see here. I tried to address this by dropping Python to 3.14 for this job (and the other -upstream-v3.9.0 jobs).

[glatterf42]

Looks good to me for the most part. Just one question about this failure that we see only on ubuntu-latest-py3.14-upstream >= 3.11.0:

FAILED message_ix_models/tests/model/transport/test_report.py::test_simulated_iamc - AssertionError: assert {'Energy Serv...nger|LDV|BEV'} <= {'Transport|S...nger|LDV|BEV'}
  
  Extra items in the left set:
  'Final Energy|Transportation|Bus'
  'Energy Service|Transportation|Domestic Aviation'

Is that expected or should/could this be fixed by this PR, too?