[FIX] Change variable check on cache condition

manifest-pipeline-yocto.yml

@@ -218,7 +218,7 @@ retrigger:
         repo sync -j$(nproc) --fetch-submodules;
         . ./seco-setup.sh -d ${DEFCONFIG_FILE};
         . ./seco-setup.sh -c;
-        if [ ! -n "$CI_COMMIT_TAG" ]; then
+        if [ -z "$CI_COMMIT_TAG" ]; then
             sed -i -e '/DL_DIR ?=/d' conf/local.conf;
             echo 'DL_DIR = \"/var/cache/edgehog_downloads\"' >> conf/local.conf;
             if [[ $PROCESSOR == *imx6* && "$CI_JOB_NAME" != *"embedded"* ]];