Bump GitHub Actions versions in install workflow

Update .github/workflows/install.yml to use actions/checkout@v6 and actions/setup-python@v6. This brings the workflow up to newer action releases for improved features, security fixes, and compatibility with current runners while retaining the existing Python matrix and install steps.

Author: kozo2

.github/workflows/install.yml

@@ -9,9 +9,9 @@ jobs:
       matrix:
         python-version: [3.11, 3.12, 3.13, 3.14]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v6
       - name: Set up Python
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v6
         with:
           python-version: '3.x'
       - name: Install dependencies