tools: update checkout action on CI

https://github.com/actions/checkout\#whats-new

Author: UltiRequiem

.github/workflows/deploy.yml

@@ -8,7 +8,7 @@ jobs:
   deploy:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         fetch-depth: 0
     - name: Install mdbook