ci: bump actions to node-24-compatible versions

actions/checkout@v4 → v5, actions/setup-python@v5 → v6.
Removes Node 20 deprecation warnings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Tools00

.github/workflows/ci.yml

@@ -16,10 +16,10 @@ jobs:
         python-version: ["3.11", "3.12", "3.13"]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python-version }}
           cache: pip
@@ -36,10 +36,10 @@ jobs:
     name: Lint (ruff)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
 
       - name: Set up Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: "3.12"
           cache: pip