CI/BLD: Build with Emscripten 6.0.5

[agriyakhetarpal]

The upcoming Pyodide 315.0 release (2026_5 ABI, and our alphas are already out: https://github.com/pyodide/pyodide/releases/tag/315.0.0a2) will use Emscripten 6.0.5. We still need to support Pyodide 314.0 with the 2026_0 ABI and Emscripten 5.0.3 for a little while longer, as pyemscripten wheels continue to gain adoption, so I decided to add a matrix.

[ilayn]

All looks good to me @agriyakhetarpal I can't say I get all the details but you are the expert on this so I don't mind. I am still going through the documentation overhaul and hoping to get it done soon so we can do a proper versioned release. I'll just make another dummy release like the previous times until then. But if you say, it is getting annoying let me know so we can do a proper versioning scheme and make a release.

[agriyakhetarpal]

Thanks @ilayn! Dummy releases work for now. These changes are mostly in preparation for SciPy 2.0 which can soon work with Pyodide 315.0.0 and I would like to make that transition smooth enough. Any choice of versioning scheme should be more than reasonable. LMK if I can probably help with anything on the documentation overhaul side and make your life easier :)