Update to 20.04 (18.04 not available now) and python 3.8, as the new …

…minimum version we use

.github/workflows/publish-to-pypi.yml

@@ -21,7 +21,7 @@ permissions:
 jobs:
   build-n-publish:
     name: Build and publish Python distributions to PyPI
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v3
@@ -31,10 +31,10 @@ jobs:
     - run: |
         git fetch origin +refs/tags/*:refs/tags/*
 
-    - name: Set up Python 3.7
+    - name: Set up Python 3.8
       uses: actions/setup-python@v4
       with:
-        python-version: 3.7
+        python-version: 3.8
 
     - name: Install pep517
       run: >-