fix pypi actions

.github/workflows/publish-on-pypi-test.yml

@@ -8,7 +8,7 @@ on:
 jobs:
   build-n-publish:
     name: Build and publish to TestPyPI
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master
     - name: Set up Python 3

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

@@ -8,7 +8,7 @@ on:
 jobs:
   build-n-publish:
     name: Build and publish to TestPyPI and PyPI
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master
     - name: Set up Python 3