update workflow

.github/workflows/pypi.yml

@@ -1,38 +1,39 @@
 name: Publish to PyPI
 on: 
+  workflow_dispatch:
   push:
     tags:
       - '*'
 
 jobs:
   build-n-publish:
     name: Build and publish to PyPI and TestPyPI
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@main
     - name: Set up Python 3.7
       uses: actions/setup-python@v1
       with:
         python-version: 3.7
 
-    - name: Install package 
+    - name: Install package
       run: |
           pip install build
 
     - name: Build source tarball
       run: |
           rm -rf dist;
           python setup.py sdist
- 
+
     - name: Publish distribution to Test PyPI
-      uses: pypa/gh-action-pypi-publish@master
+      uses: pypa/gh-action-pypi-publish@release/v1
       with:
         user: __token__
         password: ${{ secrets.TEST_PYPI_API_TOKEN }}
         repository_url: https://test.pypi.org/legacy/
     - name: Publish distribution to PyPI
       if: startsWith(github.ref, 'refs/tags')
-      uses: pypa/gh-action-pypi-publish@master
+      uses: pypa/gh-action-pypi-publish@release/v1
       with:
         user: __token__
         password: ${{ secrets.PYPI_API_TOKEN }}