chore(deps): update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/gh-pages.yml

@@ -18,7 +18,7 @@ jobs:
       url: https://kas-gui.github.io/tutorials/
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup mdBook
         uses: peaceiris/actions-mdbook@v1

.github/workflows/test.yml

@@ -14,7 +14,7 @@ jobs:
     name: Test examples
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install toolchain
         uses: actions-rs/toolchain@v1
         with: