Update CI workflow to use setup-python@v6

Author: FridrichMethod

.github/workflows/ci.yml

@@ -1,4 +1,4 @@
-name: ci
+name: CI
 
 on:
   push:
@@ -18,7 +18,7 @@ jobs:
       - uses: actions/checkout@v6
 
       - name: Set up Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python-version }}