⬆️ Upgrade setup-python GitHub Action to v2 (#3203)

.github/workflows/build-docs.yml

@@ -13,7 +13,7 @@ jobs:
         run: echo "$GITHUB_CONTEXT"
       - uses: actions/checkout@v2
       - name: Set up Python
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v2
         with:
           python-version: "3.7"
       - name: Install Flit

.github/workflows/publish.yml

@@ -15,7 +15,7 @@ jobs:
         run: echo "$GITHUB_CONTEXT"
       - uses: actions/checkout@v2
       - name: Set up Python
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v2
         with:
           python-version: "3.6"
       - name: Install Flit

.github/workflows/test.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install Flit