Update the monitoring configuration for 15.6

[danidoni]

Due to the recent upgrade of our reference instance server on https://build.opensuse.org to 15.6, we need to sync the monitoring configuration.

[eduardoj]

I found another ocurrence of 15.5, here:

kurren/lib/obs.rb

Line 30 in d52e31a

slack_message = 'Build failed for obs-server. https://build.opensuse.org/package/live_build_log/OBS:Server:Unstable/obs-server/15.5/x86_64'

[danidoni]

I found another ocurrence of 15.5, here:

kurren/lib/obs.rb

Line 30 in d52e31a

slack_message = 'Build failed for obs-server. https://build.opensuse.org/package/live_build_log/OBS:Server:Unstable/obs-server/15.5/x86_64'

Got it