ci: disable the UT for S2 when label is not used

tools/ci/config/target-test.yml

@@ -495,7 +495,8 @@ UT_034:
       - triggers
       - schedules
     variables:
-      - $BOT_TRIGGER_WITH_LABEL == null
+      # Due to lack of runners, S2 tests will only be triggered with label (@bot test will not trigger)
+      # - $BOT_TRIGGER_WITH_LABEL == null
       - $BOT_LABEL_UNIT_TEST_S2
 
 UT_035: