Limit git rev-list output count to one in forced push check

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 v 8.11.0 (unreleased)
   - Fix of 'Commits being passed to custom hooks are already reachable when using the UI'
+  - Limit git rev-list output count to one in forced push check
 
 v 8.10.0 (unreleased)
   - Fix profile activity heatmap to show correct day name (eanplatter)

lib/gitlab/checks/force_push.rb

@@ -8,8 +8,8 @@ module Gitlab
         if Gitlab::Git.blank_ref?(oldrev) || Gitlab::Git.blank_ref?(newrev)
           false
         else
-          missed_refs, _ = Gitlab::Popen.popen(%W(#{Gitlab.config.git.bin_path} --git-dir=#{project.repository.path_to_repo} rev-list #{oldrev} ^#{newrev}))
-          missed_refs.split("\n").size > 0
+          missed_ref, _ = Gitlab::Popen.popen(%W(#{Gitlab.config.git.bin_path} --git-dir=#{project.repository.path_to_repo} rev-list --max-count=1 #{oldrev} ^#{newrev}))
+          missed_ref.present?
         end
       end
     end