Bump versions of GH actions

The following obsolete GitHub action has been causing build error: actions/upload-artifact
Few other old versions have been updated as well as versions < 4 are
deprecated.

Author: gkostkowski

.github/workflows/antora-worflow.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: [ ubuntu-latest ]
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: "Install Node 16"
         uses: actions/setup-node@v3
         with:
@@ -20,7 +20,7 @@ jobs:
       - name: "Generate site using antora site action"
         run: make build-site
       - name: "Upload generated site"
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: site
           path: "${{ github.workspace }}/build/${{ env.SITE_DIR }}"
@@ -37,9 +37,9 @@ jobs:
         with:
           node-version: 16
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Download generated site
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: site
           path: "${{ github.workspace }}/${{ env.SITE_DIR }}"