update github action

Author: CarloLucibello

.github/workflows/docs.yml

@@ -11,7 +11,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@latest
         with:
           version: '1.8.2'