Fix Slack merge message spec

Signed-off-by: Rémy Coutable <remy@rymai.me>

spec/models/project_services/slack_service/merge_message_spec.rb

@@ -44,7 +44,7 @@ describe SlackService::MergeMessage, models: true do
 
     it 'returns a message regarding approval of merge requests' do
       expect(subject.pretext).to eq(
-        'Test User approved <somewhere.com/merge_requests/100|merge request !100> '\
+        'test.user approved <somewhere.com/merge_requests/100|merge request !100> '\
         'in <somewhere.com|project_name>: *Issue title*')
       expect(subject.attachments).to be_empty
     end