makefiles: quiet messages on CI

After introducing RIOT-OS#18423 there are occasional messages that still happen.
These messages cause a diff output when testing with TEST_KCONFIG=1.
This then causes a failure when comparing make/kconfig modules and packages.

makefiles/tools/kconfiglib.inc.mk

@@ -3,9 +3,13 @@ MENUCONFIG ?= $(RIOTTOOLS)/kconfiglib/riot_menuconfig.py
 BASE_MENUCONFIG ?= $(RIOTTOOLS)/kconfiglib/menuconfig.py
 GENCONFIG := $(RIOTTOOLS)/kconfiglib/genconfig.py
 
+ifeq ($(RIOT_CI_BUILD),1)
+  QUIETMESSAGES=":"
+endif
 $(BASE_MENUCONFIG):
-	@echo "[INFO] Kconfiglib not found - getting it"
+	@$(QUIETMESSAGES) echo "[INFO] Kconfiglib not found - getting it"
 	@$(MAKE) -C $(RIOTTOOLS)/kconfiglib
-	@echo "[INFO] Kconfiglib downloaded"
+	@$(QUIETMESSAGES) echo "[INFO] Kconfiglib downloaded"
+
 
 $(GENCONFIG): $(BASE_MENUCONFIG)