ci(github-actions): upgrade setup-python to v2

Author: Lee-W

.github/workflows/pythonpackage.yml

@@ -14,7 +14,7 @@ jobs:
       with:
         fetch-depth: 0
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v1
+      uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies