bump actions/checkout 2 -> 3

.github/workflows/publish-docker.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Get Docker Metadata
         id: meta

.github/workflows/push.yml

@@ -10,7 +10,7 @@ jobs:
           - 2.6
           - 2.7
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v3
     - name: script/cibuild-docker
       run: script/cibuild-docker
       env: