Fix broken "blurb" entry in properties file

Add the original `blurb` entry back with the "slave" term changed to "agente".

Part of the entry was removed in commit 05a29896,
leaving an invalid multi-line entry behind.

core/src/main/resources/jenkins/security/s2m/MasterKillSwitchWarning/message_pt_BR.properties

@@ -22,5 +22,5 @@
 
 Examine=
 Dismiss=
-# <a href="https://jenkins.io/redirect/security-144">Please read the documentation</a> and consider turning it on.
+blurb=O agente para o master security subsystem est\u00e1 desligado. \
   <a href="https://jenkins.io/redirect/security-144">Por favor leia a documenta\u00e7\u00e3o</a> e ligue novamente.