CI: changed the way we access to env var

Author: mgerhardy

.github/workflows/main.yml

@@ -74,7 +74,7 @@ jobs:
             mkdir build
             cd build
             cmake --version
-            cmake .. -DCMAKE_BUILD_TYPE=Release -DTOOLS=OFF -DUNITTESTS=OFF -DCMAKE_TOOLCHAIN_FILE=$env{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake
+            cmake .. -DCMAKE_BUILD_TYPE=Release -DTOOLS=OFF -DUNITTESTS=OFF -DCMAKE_TOOLCHAIN_FILE=$VCPKG_ROOT/scripts/buildsystems/vcpkg.cmake
             cmake --build .
             cmake --install . --component caveexpress --prefix install-caveexpress
             cmake --install . --component cavepacker --prefix install-cavepacker