ci: refactor tests package test script

Check suffix directly, and fix indentation

.ci/build_packages/tests.sh

@@ -69,8 +69,7 @@ emqx_prepare(){
 emqx_test(){
     cd "${PACKAGE_PATH}"
     local packagename="${PACKAGE_FILE_NAME}"
-
-        case ${packagename##*.} in
+    case "$PKG_SUFFIX" in
         "zip")
             unzip -q "${PACKAGE_PATH}/${packagename}"
             export EMQX_ZONE__EXTERNAL__SERVER__KEEPALIVE=60 \
@@ -147,7 +146,6 @@ emqx_test(){
                 exit 1
             fi
         ;;
-
     esac
 }