chore(deps): update actions/setup-python action to v3 (#1359)

Author: busunkim96

synthtool/gcp/templates/python_library/.github/workflows/docs.yml

@@ -10,7 +10,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v2
     - name: Setup Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: "{{ unit_test_python_versions | last }}"
     - name: Install nox
@@ -26,7 +26,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v2
     - name: Setup Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: "{{ unit_test_python_versions | last }}"
     - name: Install nox

synthtool/gcp/templates/python_library/.github/workflows/lint.yml

@@ -10,7 +10,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v2
     - name: Setup Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: "{{ unit_test_python_versions | last }}"
     - name: Install nox

synthtool/gcp/templates/python_library/.github/workflows/unittest.yml

@@ -13,7 +13,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v2
     - name: Setup Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: ${{ '{{' }} matrix.python {{ '}}' }}
     - name: Install nox
@@ -39,7 +39,7 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v2
     - name: Setup Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v3
       with:
         python-version: "{{ unit_test_python_versions | last }}"
     - name: Install coverage