Update outdated actions

Author: TimoRoth

.github/workflows/build-pages.yml

@@ -19,7 +19,7 @@ jobs:
     container: ghcr.io/oggm/oggm:latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Fix git permission check
         run: git config --global --add safe.directory "$GITHUB_WORKSPACE"
       - name: Cache
@@ -41,7 +41,7 @@ jobs:
         run: |
           jupyter-book build .
       - name: Upload Build Artifacts
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: build-output
           path: _build/