[rwgk]

Description

Fix CI setup failures exposed by #6208: pin the Python 3.9 Linux jobs to Ubuntu 24.04 and explicitly enable Pyodide cross-compilation so CMake does not try to run the host interpreter through Node. Update cibuildwheel to 4.3.4 for the eMudhra certificate mitigations.

Validation: prek -a --quiet; CMake 4.4.4 cross-compilation probe reproduces the old failure and passes with the setting enabled; local Pyodide 314.0.7 wheel build/tests with CMake 4.4.4 (1,242 passed, 192 skipped, 2 xfailed, 1 xpassed).

Suggested changelog entry:

• Updated CI runners and cross-compilation tooling, including updated certificate mitigations.

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codex GPT-6.1-Sol ultra on behalf of Ralf

[rwgk]

@henryiii codex GPT-6.1-Sol ultra explained:

This fixes the Pyodide cross-build’s Python discovery failure. The original job stopped during configuration with Could NOT find Python (missing: Interpreter).

The interaction was:

1. Emscripten sets Node as the cross-compilation emulator.
2. Without this flag, pybind11 requests both Interpreter and Development.Module.
3. Under CMake’s CMP0190 policy, that combination makes CMake execute the interpreter through the emulator. Here, it tried to run native Python through Node.

The subtlety is that our automatic cross-compilation default only activates when no emulator is defined, so Pyodide needs the explicit opt-in.

PYBIND11_USE_CROSSCOMPILING=ON activates the existing logic that omits interpreter discovery. The pyodide.config-settings scope applies it specifically to Pyodide wheel builds.

I reproduced configuration failing with OFF and succeeding with ON, then verified the full Pyodide build and test run.

[rwgk]

Merging without a review under the bitrot category.