[3.14] gh-146197: Add Emscripten to CI (GH-146198)

[hoodmane]

(cherry picked from commit c94048b)

• Issue: Add CI job for Emscripten #146197

[hoodmane]

!buildbot emscripten

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @hoodmane for commit 68bbcec 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F146331%2Fmerge

The command will test the builders whose names match following regular expression: emscripten

The builders matched are:

• WASM Emscripten PR

[hoodmane]

@hugovk if this looks okay to you would appreciate a merge.

[vstinner]

I clicked on [Update branch]. Previously, the branch was outdated. For example, Platforms/emscripten/config.toml didn't contain pythoninfo-args.

[vstinner]

The "Tests / Emscripten / build and test" CI job has the "Display build info" step as expected. Example:

sys._emscripten_info: sys._emscripten_info(emscripten_version=(4, 0, 12), runtime='Node.js/24', pthreads=False, shared_memory=False)