tests: Avoid action's warning

Author: jcs090218

.github/workflows/docs.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: MkDocs
         run: |

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
           - snapshot
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
 
     - uses: jcs090218/setup-emacs@master
       with: