Update apt repos before installing

This should fix the error seen in
https://github.com/AliceO2Group/O2DPG/runs/1430098425.

Author: TimoWilken

.github/workflows/release.yml

@@ -10,6 +10,7 @@ jobs:
     steps:
     - name: Install Kerberos
       run: |
+        sudo apt-get update
         sudo DEBIAN_FRONTEND=noninteractive apt-get install -y krb5-user
         cat << \EOF > krb5.conf
         ${{secrets.KRB5CONF}}