ci: fetching the gh-pages branch added to the documentation GitHub Action

.github/workflows/documentation.yml

@@ -47,10 +47,11 @@ jobs:
       - name: Installing pip packages
         run: |
           pip install conan mkdocs-material mike
-      - name: Setup git configuration
+      - name: Prepare git
         run: |
           git config --global user.name github-actions
           git config --global user.email github-actions@github.com
+          git fetch origin gh-pages --depth=1
       - name: Building docs
         run: |
           mike deploy --push --update-aliases `conan inspect .  | sed -n -r 's/version: ([0-9]+.[0-9]+).[0-9]+/\1/p'` latest