Notify only when unmergeable due to conflict

There is still the edge case when 'no commits' changes to 'conflict'
would not trigger notification, which we ignore for now.

Calling can_be_merged? can cause exception (e.g. non-UTF8)
Ignore those by rescueing.

Remove unmergeable_reason as now only conflict is notified

Update spec

1 files changed, 1 insertions, 7 deletions

diff --git a/spec/mailers/notify_spec.rb b/spec/mailers/notify_spec.rb
index 775ca4ba0eb..a9a45367b4a 100644
--- a/spec/mailers/notify_spec.rb
+++ b/spec/mailers/notify_spec.rb
@@ -416,16 +416,10 @@ describe Notify do
         end
 
         it 'has the correct subject and body' do
-          reasons = %w[foo bar]
-
-          allow_any_instance_of(MergeRequestPresenter).to receive(:unmergeable_reasons).and_return(reasons)
           aggregate_failures do
             is_expected.to have_referable_subject(merge_request, reply: true)
             is_expected.to have_body_text(project_merge_request_path(project, merge_request))
-            is_expected.to have_body_text('following reasons:')
-            reasons.each do |reason|
-              is_expected.to have_body_text(reason)
-            end
+            is_expected.to have_body_text('due to conflict.')
           end
         end
       end