[CI] fix /nix dir permissions

Apparently, this is needed to run 'nix' inside tests (e.g. start corenlp)

.gitlab-ci.yml

@@ -73,6 +73,12 @@ test:
     - chown -R test:test ${CABAL_DIR}
     - mkdir -p "$XDG_CACHE_HOME/nix"
     - chown -R test:test "$XDG_CACHE_HOME/nix"
+    # Fix
+    # opening lock file '/nix/var/nix/db/big-lock': Permission denied
+    # when starting CoreNLP
+    - chmod -R 755 /nix/var/nix/db/
+    - chmod 666 /nix/var/nix/db/big-lock
+
 
   cache:
     key: cabal.project