Fix Error 500s when attempting to destroy a protected tag

Due to a missing `on_delete: :cascade`, users would hit the error that
looked like:

```
PG::ForeignKeyViolation: ERROR: update or delete on table "protected_tags"
violates foreign key constraint "fk_rails_f7dfda8c51" on table
"protected_tag_create_access_levels" DETAIL: Key (id)=(1385) is still
referenced from table "protected_tag_create_access_levels". : DELETE FROM
"protected_tags" WHERE "protected_tags"."id" = 1385
```

Closes #36013

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/gitlab/database/migration_helpers.rb b/lib/gitlab/database/migration_helpers.rb
index 69ca9aa596b..b83e633c7ed 100644
--- a/lib/gitlab/database/migration_helpers.rb
+++ b/lib/gitlab/database/migration_helpers.rb
@@ -606,6 +606,11 @@ module Gitlab
           Arel::Nodes::SqlLiteral.new(replace.to_sql)
         end
       end
+
+      def remove_foreign_key_without_error(*args)
+        remove_foreign_key(*args)
+      rescue ArgumentError
+      end
     end
   end
 end