Fix gh pages deployment

Author: bash

.github/workflows/docs.yml

@@ -23,7 +23,7 @@ jobs:
       working-directory: ./documentation
     - name: Deploy
       uses: peaceiris/actions-gh-pages@v3
-      if: success() && github.ref == 'refs/heads/master'
+      if: success() && github.ref == 'refs/heads/main'
       with:
         github_token: ${{secrets.GITHUB_TOKEN}}
         publish_dir: ./documentation/book