Fix publish.yml

Author: Sebastian Simon

.github/workflows/publish.yml

@@ -1,4 +1,4 @@
-name: Python package
+name: Publish Python package
 on:
   push:
     tags:
@@ -7,10 +7,11 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/checkout@v3
       - name: Build and publish to pypi
         uses: JRubics/[email protected]
         with:
-          python_version: "3.7.1"
+          python_version: "3.9"
           pypi_token: ${{ secrets.PYPI_TOKEN }}