Update ci.yml

Fix if statement

Author: fjp

.github/workflows/ci.yml

@@ -34,5 +34,5 @@ jobs:
       - name: build documentation
         run: mkdocs build
       - name: deploy documentation
-        if: ${{ github.ref == 'main' }}
+        if: ${{ github.ref == 'refs/heads/main' }}
         run: mkdocs gh-deploy --force