Bump actions/checkout from 2 to 3 (#866)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Ovidiu Voda <ovi.voda@gmail.com>

.github/workflows/gh-pages-mdbook.yml

@@ -8,7 +8,7 @@ jobs:
     name: Build
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: extractions/setup-just@v1
       - name: Setup mdBook
         uses: peaceiris/actions-mdbook@v1
@@ -29,7 +29,7 @@ jobs:
     name: Deploy
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Download book
         uses: actions/download-artifact@v3
         with: