Fix top_scope_facts lint violation

This is not a fact, but rather a global variable. Using getvar is the
right way here, like all other variables in this file.

Author: ekohl

manifests/plugin/remote_execution/ssh_user/params.pp

@@ -13,7 +13,7 @@
   $effective_user_method = pick(getvar('remote_execution_effective_user_method'),'sudo')
 
   $ssh_keys = getvar('remote_execution_ssh_keys') ? {
-    Array   => $::remote_execution_ssh_keys,
+    Array   => getvar('remote_execution_ssh_keys'),
     default => [],
   }
 }