Fix setup step in Build and Cassandra workflows

The workflows fail for current pull requests as it seems that
xenial-security does not maintain keys for the Ubuntu keyserver.
This will manually add the keys to the system.

Author: Gor027

.github/workflows/build.yml

@@ -22,6 +22,8 @@ jobs:
 
     - name: Setup environment
       run: |
+        sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
+        sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
         sudo sh -c "echo 'deb http://security.ubuntu.com/ubuntu xenial-security main' >> /etc/apt/sources.list"
         sudo apt-get update
         sudo apt-get install libssl1.0.0 libuv1-dev libkrb5-dev libc6-dbg

.github/workflows/cassandra.yml

@@ -28,6 +28,8 @@ jobs:
 
       - name: Setup environment
         run: |
+          sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
+          sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
           sudo sh -c "echo 'deb http://security.ubuntu.com/ubuntu xenial-security main' >> /etc/apt/sources.list"
           sudo apt-get update
           sudo apt-get install libssl1.0.0 libuv1-dev libkrb5-dev libc6-dbg