Action fails to install older emscripten version due to mismatch between emsdk `main` and tagged emscripten versions

[akien-mga]

See https://github.com/emscripten-core/emsdk/issues/1379 for context, there's been a change to filenames for some of the artifacts downloaded by emsdk, and somehow this started breaking stuff today.

The upstream recommendation is that for a given emscripten version, one should use the matching emsdk version, but this action always downloads the latest emsdk main branch:

https://github.com/mymindstorm/setup-emsdk/blob/6ab9eb1bda2574c4ddb79809fc9247783eaf9021/src/main.ts#L50

I would suggest changing this to follow the version config, so if e.g. requesting emscripten 3.1.39, it would download https://github.com/emscripten-core/emsdk/archive/3.1.39.zip

This could be made configurable via a emsdk_version that could default to the same value as version, but could be overridden to e.g. main if someone knows they need latest emsdk regardless of the emscripten version they request.