Fix failing xeus-cpp build

Author: anutosh491

.github/workflows/emscripten.yml

@@ -596,9 +596,10 @@ jobs:
         pushd build
         emcmake cmake \
           -DCMAKE_BUILD_TYPE=${{ env.BUILD_TYPE }}          \
+          -DCMAKE_PREFIX_PATH=${{ env.PREFIX }}             \
           -DCMAKE_INSTALL_PREFIX=${{ env.PREFIX }}          \
           -DXEUS_CPP_EMSCRIPTEN_WASM_BUILD=ON               \
-          -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=${{ env.PREFIX }}               \
+          -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ON               \
           -DCppInterOp_DIR="${{ env.CPPINTEROP_BUILD_DIR }}/lib/cmake/CppInterOp"  \
           -DSYSROOT_PATH=$SYSROOT_PATH                      \
           ..