CI: imscripten fastcomp backend is now deprecated (#3402)

Fastcomp backend was introduced here: https://github.com/ocornut/imgui/commit/14b18697e653de80f75af18113033b2086846194
Emscripten changelog: https://emscripten.org/docs/introducing_emscripten/release_notes.html?highlight=2.0.0:%2008/10/2020
Emscripten issue: https://github.com/emscripten-core/emsdk/pull/590

Updated CHANGELOG.txt
2 files changed