Python doc: do not release as "stable" for beta versions

.github/workflows/release.yml

@@ -194,9 +194,9 @@ jobs:
           path: website
           token: ${{ secrets.FULL_ACCESS_TOKEN }}
       - run: echo "RELEASE_VERSION=$(echo ${GITHUB_REF:10})" >> $GITHUB_ENV
-      - run: |
-          rm -rf ./website/pyoxigraph/stable && mkdir -p ./website/pyoxigraph/stable && cp -r ./python/docs/build/html/* ./website/pyoxigraph/stable/
-          mkdir -p ./website/pyoxigraph/$RELEASE_VERSION && cp -r ./python/docs/build/html/* ./website/pyoxigraph/$RELEASE_VERSION/
+      - run: rm -rf ./website/pyoxigraph/stable && mkdir -p ./website/pyoxigraph/stable && cp -r ./python/docs/build/html/* ./website/pyoxigraph/stable/
+        if: ${{ !contains('-', github.event.release.tag_name) }}
+      - run: mkdir -p ./website/pyoxigraph/$RELEASE_VERSION && cp -r ./python/docs/build/html/* ./website/pyoxigraph/$RELEASE_VERSION/
       - run: |
           git config user.name github-actions
           git config user.email github-actions@github.com