ci: emscripten builds are failing with Emscripten SDK 3.1.58

[przemoc]

Error copying file "/home/runner/work/whisper.cpp/whisper.cpp/bin/libwhisper.worker.js" to "/home/runner/work/whisper.cpp/whisper.cpp/bindings/javascript/libwhisper.worker.js".

Looking at older passing vs newer failing runs, we may notice that Emscripten SDK version changed from 3.1.57 to 3.1.58. In ChangeLog for Emscripten SDK 3.1.58 we may see they refer to changes with handling of .worker.js, which may be the reason of the failure:

• Multi-threaded builds no depend on a separate .worker.js file. This saves
  on code size and network requests. In order to make this change go smoothly,
  without breaking build systems that expect a worker.js, emscripten will
  generate an empty .worker.js to give folks time to transition their
  deployment scripts. In -sSTRICT mode, this empty file will not be
  generated. (#21701)

There seem to be various follow-up improvements to this change that will be part of 3.1.59, so delaying working on it may be the most efficient way to deal with this issue by whoever will want to fix it.

[przemoc]

Recent run in CI is using Emscripten SDK 3.1.59, where issue is no longer observed.