Update documentation-ci.yml

Use version 6.2.0 as it failed when trying using sphinx version >= 7.0.0

.github/workflows/documentation-ci.yml

@@ -17,7 +17,7 @@ jobs:
       uses: actions/checkout@v3
     - name: Build the Documentation using sphinx Docker image
       run: |
-        docker run --rm -v $(pwd)/docs:/docs sphinxdoc/sphinx make html ;
+        docker run --rm -v $(pwd)/docs:/docs sphinxdoc/sphinx:6.2.0 make html ;
         sudo touch docs/_build/html/.nojekyll ;
         sudo cp docs/_config.yml docs/_build/html/
     - name: Build the Documentation using doxygen Docker image