PSA: version reported by `main` branch is moving to forward looking version

[Sam Clegg]

If you don't use emscripten from a git chckout yon can stop reading now.

We are switching to a model more like llvm where the `main` branch reports itself to be the "next" version which is yet to be released.  See: https://github.com/emscripten-core/emscripten/pull/14091

Previously we would report the version of the last release.  Either way this information is never completely accurate if you are on `main` since `main` is constantly changing.

Hopefully this should not be something that affects most users.  Please let us know if it does.

cheers,

sam,