fix: downgrade CI actions to stable v4/v5, fix YAML indentation

Author: Coding-Dev-Tools

.github/workflows/ci.yml

@@ -1,10 +1,10 @@
 name: CI
 
 on:
-push:
-  branches: [main]
-pull_request:
-  branches: [main]
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
 
 permissions:
   contents: read
@@ -17,12 +17,12 @@ jobs:
         python-version: ["3.10", "3.11", "3.12", "3.13"]
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v4
         with:
           persist-credentials: false
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v6
+        uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}