ci: use manual git clone for CentOS 7 container

actions/checkout@v3 requires Node.js 20 which needs glibc 2.25+,
but CentOS 7 only has glibc 2.17. Use manual git clone instead.

Author: dvershinin

.github/workflows/test.yml

@@ -19,16 +19,14 @@ jobs:
           sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*.repo
           sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*.repo
 
-      - name: Install git
-        run: yum -y install git
+      - name: Install git and dependencies
+        run: yum -y install git python2 python2-pip python-six
 
-      - name: Checkout code
-        uses: actions/checkout@v3
+      - name: Clone repository
+        run: git clone --depth 1 --branch ${{ github.ref_name }} https://github.com/${{ github.repository }}.git .
 
-      - name: Install dependencies
-        run: |
-          yum -y install python2 python2-pip python-six
-          pip2 install netaddr
+      - name: Install Python dependencies
+        run: pip2 install netaddr
 
       - name: Verify Python 2.7 imports
         run: |