ci(workflows): update GitHub Actions to v6

This updates the checkout and Python setup steps in CI to use newer major versions.

It keeps the workflows compatible with the latest supported GitHub Actions releases.

Author: asyrjasalo

.github/workflows/atest.yml

@@ -14,13 +14,13 @@ jobs:
         python-version: [3.11, 3.12, 3.13, 3.14]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Setup Node.js
-        uses: actions/setup-node@v4
+        uses: actions/setup-node@v6
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python-version }}
 

.github/workflows/build.yml

@@ -14,10 +14,10 @@ jobs:
         python-version: [3.11, 3.12, 3.13, 3.14]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python-version }}
 

.github/workflows/test.yml

@@ -14,10 +14,10 @@ jobs:
         python-version: [3.11, 3.12, 3.13, 3.14]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.python-version }}