[gitlab-ci] Fix test-with-stats

The EMPER option Meson option for stats is called 'stats' not
'worker_stats'.

.gitlab-ci.yml

@@ -93,9 +93,9 @@ clang-tidy:
   variables:
     EMPER_WORKER_SLEEP: 'false'
 
-.emper-worker-stats:
+.emper-stats:
   variables:
-    EMPER_WORKER_STATS: 'true'
+    EMPER_STATS: 'true'
 
 .emper-userspace-rcu:
   variables:
@@ -201,7 +201,7 @@ test-worker-no-sleep:
 test-with-stats:
   extends:
     - .test
-    - .emper-worker-stats
+    - .emper-stats
 
 test-with-userspace-rcu:
   extends: