Merge branch 'fix-check-constraint-removal-for-has_external_wiki' into 'master'

Verify check constraint existence before removing

See merge request gitlab-org/gitlab!53267

db/migrate/20210203092540_remove_has_external_wiki_constraint.rb

@@ -9,8 +9,10 @@ class RemoveHasExternalWikiConstraint < ActiveRecord::Migration[6.0]
 
   def up
     # This reverts the following migration: add_not_null_constraint :projects, :has_external_wiki, validate: false
+    if check_not_null_constraint_exists?(:projects, :has_external_wiki)
       remove_not_null_constraint :projects, :has_external_wiki
     end
+  end
 
   def down
     # no-op