Merge branch 'rails5-fix-48104' into 'master'

Rails5 fix expected: 1 time with arguments: (97, anything, {"squash"=>false}) received: 0 times

Closes #48104

See merge request gitlab-org/gitlab-ce!20004

changelogs/unreleased/rails5-fix-48104.yml

+---
+title: 'Rails5 fix expected: 1 time with arguments: (97, anything, {"squash"=>false})
+  received: 0 times'
+merge_request: 20004
+author: Jasper Maes
+type: fixed

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -337,7 +337,12 @@ describe Projects::MergeRequestsController do
 
     context 'when the sha parameter matches the source SHA' do
       def merge_with_sha(params = {})
-        post :merge, base_params.merge(sha: merge_request.diff_head_sha).merge(params)
+        post_params = base_params.merge(sha: merge_request.diff_head_sha).merge(params)
+        if Gitlab.rails5?
+          post :merge, params: post_params, as: :json
+        else
+          post :merge, post_params
+        end
       end
 
       it 'returns :success' do