message: chore(ci): fix vercel build
  By checking for a specific file existence, not directory existence, when deciding on whether to install emsdk
diff: @@ -626,7 +626,7 @@ echo "-------------------------------------------------------------------------"
  if [ "${NEXTCLADE_BUILD_WASM}" == "true" ] || [ "${NEXTCLADE_BUILD_WASM}" == "1" ]; then
  print 92 "Install Emscripten SDK";
  - if [ ! -d "${NEXTCLADE_EMSDK_DIR}" ]; then
  + if [ ! -f "${NEXTCLADE_EMSDK_DIR}/emsdk_env.sh" ]; then
  ./scripts/install_emscripten.sh "${NEXTCLADE_EMSDK_DIR}" "${NEXTCLADE_EMSDK_VERSION}"
  else
  echo "Emscripten SDK already found in '${NEXTCLADE_EMSDK_DIR}'. Skipping install."
  