Update build.yml to use vault repo for centos7

Author: NadeemYaseen

.github/workflows/build.yml

@@ -80,6 +80,8 @@ jobs:
 
       - name: Install ssh-agent
         run: |
+          yum-config-manager --disable base extras updates
+          yum-config-manager --enable C7.9.2009-base C7.9.2009-updates C7.9.2009-extras 
           yum install -y openssh-server openssh-clients
           yum-config-manager --enable rhel-server-rhscl-7-rpms
           yum install -y https://repo.ius.io/ius-release-el7.rpm