Update GHA

* actions/checkout@v3 -> actions/checkout@v4
* actions/download-artifact@v3 -> actions/download-artifact@v4
* actions/upload-artifact@v3 -> actions/upload-artifact@v4

For more information see:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

.github/workflows/docbook.yml

@@ -22,7 +22,7 @@ jobs:
       allow-build: ${{ steps.select-dc-build.outputs.allow-build }}
       relevant-branches: ${{ steps.select-dc-build.outputs.relevant-branches }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Checking basic soundness of DC files
         uses: openSUSE/doc-ci@gha-select-dcs
@@ -51,7 +51,7 @@ jobs:
       matrix:
         dc-files: ${{ fromJson(needs.select-dc-files.outputs.validate-list) }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Validating DC file(s) ${{ matrix.dc-files }}
         uses: openSUSE/doc-ci@gha-validate
         with:
@@ -69,14 +69,14 @@ jobs:
       matrix:
         dc-files: ${{ fromJson(needs.select-dc-files.outputs.build-list) }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Building DC file(s) ${{ matrix.dc-files }}
         id: build-dc
         uses: openSUSE/doc-ci@gha-build
         with:
           dc-files: ${{ matrix.dc-files }}
       - name: Uploading builds as artifact
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: ${{ steps.build-dc.outputs.artifact-name }}
           path: ${{ steps.build-dc.outputs.artifact-dir }}/*
@@ -90,7 +90,7 @@ jobs:
     continue-on-error: true
     steps:
       - name: Downloading all build artifacts
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           path: artifact-dir
       - name: Publishing builds on susedoc.github.io