Fix "build and push stable image" jobs not running on develop/master branches

Failing jobs could be found here:

• https://gitlab.syncad.com/hive/clive/-/jobs/610423
• https://gitlab.syncad.com/hive/clive/-/jobs/610424

After these changes (tagged with temporary -testing postfix):

• https://gitlab.syncad.com/hive/clive/-/jobs/611037
• https://gitlab.syncad.com/hive/clive/-/jobs/611038