upgrade checkout from v3 to v4 to resolve CI issues

Author: alex0207s

.github/workflows/gas-diff.yml

@@ -17,7 +17,7 @@ jobs:
         node-version: [16.x]
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: recursive
 

.github/workflows/tokenlon-contracts.yml

@@ -14,7 +14,7 @@ jobs:
         node-version: [16.x]
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
         with:
           submodules: recursive
       - name: Use Node.js ${{ matrix.node-version }}