CI: Reduce threads for maltparsing

otherwise oom error
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index f8ecbc8..042feb6 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -92,8 +92,8 @@
     - start_section building_index "Building index"
     - touch target/*.zip # ignore timestamps in make
     - sleep 1
-    - touch target/*.ud.zip
-    - make -j $(nproc) target/dnb.index.tar.xz
+    - touch target/*.*.zip
+    - MAX_THREADS=2 make -j $(nproc) target/dnb.index.tar.xz
     - end_section building_krill
   artifacts:
     paths: