Ignore column MergeRequest#assignee_id

After implementing https://gitlab.com/gitlab-org/gitlab-ce/issues/59457 the step of ignoring the column was missing.

Here are the steps which need to be implemented in order to ignore and drop the MergeRequest#assignee_id column

Before doing this we need the following issues to be addressed:

Edited Aug 14, 2020 by 🤖 GitLab Bot 🤖