slaprunner and seleniumserver: Use ecdsa SSH keys in tests

After upgrade to OpensSSH 8.8p1 the simple ssh-rsa keys are not accepted
anymore.
7 jobs for feat/debian11 in 0 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:26:53

passed SlapOS.Eggs.UnitTest-Master.Python3

00:09:39

passed SlapOS.SlapRunner.ResilienceTest-Master

00:37:36

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

08:02:24

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

06:27:15

passed SlapOS.Eggs.UnitTest-Master.Python3

00:10:54

passed SlapOS.Eggs.UnitTest-Master.Python3

00:15:59