[linux-ci.yml] update actions/setup-python to v4 release line

Author: chrissimpkins

.github/workflows/linux-ci.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Check out source repository
         uses: actions/checkout@v3
       - name: Set up Python ${{ matrix.python-version }} environment
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
       - name: Python environment report