php.buildComposerProject: add missing COMPOSER_ROOT_VERSION env var.

This is mostly required for vimeo/psalm
It doesn't harm anything to add it anyway

pkgs/build-support/php/hooks/composer-repository-hook.sh

@@ -17,6 +17,7 @@ composerRepositoryConfigureHook() {
     fi
 
     if [[ ! -f "composer.lock" ]]; then
+        COMPOSER_ROOT_VERSION="${version}" \
         composer \
             --no-ansi \
             --no-install \