Update emscripten.yml

Author: mcbarton

.github/workflows/emscripten.yml

@@ -823,7 +823,7 @@ jobs:
         echo "CPPINTEROP_DIR=$env:CPPINTEROP_DIR" >> $GITHUB_ENV
         echo "LLVM_BUILD_DIR=$env:LLVM_BUILD_DIR" >> $GITHUB_ENV
         echo "CPLUS_INCLUDE_PATH=$env:CPLUS_INCLUDE_PATH" >> $GITHUB_ENV
-        echo "PREFIX=$env:PREFIX" >> $env:GITHUB_ENV
+        echo "PREFIX=$env:PREFIX" >> $GITHUB_ENV
 
     - name: Build and Test/Install CppInterOp on Windows systems (static library)
       continue-on-error: true