GA: Try different variable syntax.

.github/workflows/build.yml

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 879bccd..442f785 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -35,7 +35,7 @@
         if: ${{ runner.os == 'Windows' }}
         working-directory: ${{runner.workspace}}/build
         run: |
-          cmake -DCMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/vcpkg.cmake ${{github.workspace}}
+          cmake -DCMAKE_TOOLCHAIN_FILE=${{Env:VCPKG_ROOT}}/vcpkg.cmake ${{github.workspace}}
       - name: build
         working-directory: ${{runner.workspace}}/build
         run: |