Update GitHub Actions workflow

.github/workflows/main.yml

@@ -4,18 +4,15 @@ on: [push, pull_request]
 
 jobs:
   build:
-    runs-on: ${{ matrix.platform }}
-    strategy:
-      matrix:
-        platform: [ubuntu-22.04]
+    runs-on: ubuntu-22.04
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
         with:
           submodules: recursive
 
-      - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2.2.2
+      - name: Set up Python 2.7
+        uses: actions/setup-python@v5
         with:
           python-version: 2.7