Update spinach specs to explicitly check Remove Source Branch.

features/project/merge_requests/accept.feature

@@ -7,6 +7,7 @@ Feature: Project Merge Requests Acceptance
   @javascript
   Scenario: Accepting the Merge Request and removing the source branch
     Given I am on the Merge Request detail page
+    When I check the "Remove source branch" option
     And I click on Accept Merge Request
     Then I should see merge request merged
     And I should not see the Remove Source Branch button
@@ -14,6 +15,7 @@ Feature: Project Merge Requests Acceptance
   @javascript
   Scenario: Accepting the Merge Request when URL has an anchor
     Given I am on the Merge Request detail with note anchor page
+    When I check the "Remove source branch" option
     And I click on Accept Merge Request
     Then I should see merge request merged
     And I should not see the Remove Source Branch button
@@ -21,7 +23,6 @@ Feature: Project Merge Requests Acceptance
   @javascript
   Scenario: Accepting the Merge Request without removing the source branch
     Given I am on the Merge Request detail page
-    When I click on "Remove source branch" option
     When I click on Accept Merge Request
     Then I should see merge request merged
     And I should see the Remove Source Branch button

features/steps/project/merge_requests/acceptance.rb

@@ -11,10 +11,14 @@ class Spinach::Features::ProjectMergeRequestsAcceptance < Spinach::FeatureSteps
     visit merge_request_path(@merge_request, anchor: 'note_123')
   end
 
-  step 'I click on "Remove source branch" option' do
+  step 'I uncheck the "Remove source branch" option' do
     uncheck('Remove source branch')
   end
 
+  step 'I check the "Remove source branch" option' do
+    check('Remove source branch')
+  end
+
   step 'I click on Accept Merge Request' do
     click_button('Merge')
   end