Upgrade upload-pages-artifact to v3

upload-pages-artifact v1 uses a version of upload-artifact which is no longer supported. Attempt to bump to the latest. Unfortunately the stage deploy doesn't use this action/lib, so this cannot be tested there first.

.github/workflows/deploy.yml

@@ -74,7 +74,7 @@ jobs:
         run: echo ${{ inputs.ref }} > ./_site/ref.txt; grep .*[^\s\n\r].* ./_site/ref.txt || echo $GITHUB_REF > ./_site/ref.txt
 
       - name: Store newly built files as artifact of workflow run
-        uses: actions/upload-pages-artifact@v1
+        uses: actions/upload-pages-artifact@v3
 
   deploy:
     runs-on: ubuntu-22.04