Fix GitHub pages

As `peaceiris/actions-gh-pages` README describes, the `permissions / contents / write` definition is required. In other hand, without that, the step will fail. Also a jump to the version 4 is recommended. Basically because i did a test and previous version, as-is doesn't work.

.github/workflows/documentation.yaml

@@ -8,6 +8,9 @@ on:
 env:
   CPM_SOURCE_CACHE: ${{ github.workspace }}/cpm_modules
 
+permissions:
+  contents: write
+
 jobs:
   build:
     name: Build and publish documentation
@@ -31,7 +34,7 @@ jobs:
           cmake --build build --target GenerateDocs
 
       - name: Publish
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./build/doxygen/html