polkit-qt6: pass -DBUILD_WITH_QT6=ON

The recipe is the Qt6 build of polkit-qt-1 but the upstream CMakeLists defaults
QT_MAJOR_VERSION to 5 unless BUILD_WITH_QT6=ON, so it was looking for Qt5 and
failing. (Next blocker: it still needs libpolkit-gobject-1, the polkit client
library, which redbear-polkit — a D-Bus daemon — does not provide.)

local/recipes/libs/polkit-qt6/recipe.toml

@@ -59,6 +59,7 @@ rm -rf CMakeFiles
 cmake "${COOKBOOK_SOURCE}" \
     -DCMAKE_TOOLCHAIN_FILE="${COOKBOOK_ROOT}/local/recipes/qt/redox-toolchain.cmake" \
     -DQT_HOST_PATH="${HOST_BUILD}" \
+    -DBUILD_WITH_QT6=ON \
     -DCMAKE_INSTALL_PREFIX=/usr \
     -DCMAKE_BUILD_TYPE=Release \
     -DCMAKE_PREFIX_PATH="${COOKBOOK_SYSROOT}" \