fix build script so it actually passes along mod_loader variable

.github/workflows/build.yml

@@ -44,6 +44,7 @@ jobs:
           export `sed -e '/^#/d' -e '/^org/d' gradle.properties`
           echo "mod_version=$mod_version" >> $GITHUB_ENV
           echo "minecraft_version=$minecraft_version" >> $GITHUB_ENV
+          echo "mod_loader=$mod_loader" >> $GITHUB_ENV
       - name: Publich to Modrinth and CurseForge
         uses: Kir-Antipov/[email protected]
         with: