ci: fix CI fail (#818)

* ci: fix CI fail

* ci: fix CI fail

* ci: fix CI fail

Author: nic-chen

.github/workflows/backend-unit-test.yml

@@ -38,9 +38,9 @@ jobs:
           go-version: '1.13'
 
       - name: setup lua
-        uses: leafo/gh-actions-lua@v7
-        with:
-          luaVersion: "5.1.5"
+        run: |
+          sudo apt-get update
+          sudo apt-get install lua5.1
 
       - name: run test
         run: |