Don't ignore conflicts in db/schema.rb

It's not entirely clear to me why we were ignoring db/schema.rb in the
first place, but this should not be done now that we merge CE into EE
automatically. Doing so can lead to changes being thrown away in the
event of a conflict, which can then lead to EE pipelines failing.

lib/gitlab/ee_compat_check.rb

@@ -7,7 +7,7 @@ module Gitlab
     CANONICAL_CE_PROJECT_URL = 'https://gitlab.com/gitlab-org/gitlab-ce'.freeze
     CANONICAL_EE_REPO_URL = 'https://gitlab.com/gitlab-org/gitlab-ee.git'.freeze
     CHECK_DIR = Rails.root.join('ee_compat_check')
-    IGNORED_FILES_REGEX = %r{VERSION|CHANGELOG\.md|db/schema\.rb}i.freeze
+    IGNORED_FILES_REGEX = /VERSION|CHANGELOG\.md/i.freeze
     PLEASE_READ_THIS_BANNER = %Q{
       ============================================================
       ===================== PLEASE READ THIS =====================