Fix Jenkins condition in entry file

Follows-up 6be762858a.

The error message was, for all intends and purposes, unreachable.

Local installs and production, naturally, don't set any non-standard
variable "wgWikimediaJenkinsCI". Thus the condition was never reached.

Within Jenkins, the variable is set (with value true). Thus the
condition isn't reached there, either.

Change-Id: I29d7929aa82d5635c75bb7ea741440af0450e6e4