Build linux wheels for python 3.9.

.github/workflows/pythonpublish.yml

@@ -43,6 +43,8 @@ jobs:
       if: "matrix.os != 'ubuntu-latest'"
     - name: Build and publish (Linux)
       uses: RalfG/python-wheels-manylinux-build@v0.3.1
+      with:
+        python-versions: 'cp36-cp36m cp37-cp37m cp38-cp38 cp39-cp39'
       env:
         # Temporary fix for LD_LIBRARY_PATH issue. See
         # https://github.com/RalfG/python-wheels-manylinux-build/issues/26