Missing primary keys in custom tables

Problem/Motivation

The "email_login_otp" and "otp_settings" tables do not have a primary key, which causes an error to appear in the status report.

Steps to reproduce

• Set the MySQL transaction isolation level to "READ COMMITTED" as recommended in https://www.drupal.org/docs/getting-started/system-requirements/setting-... →
• Head over to /admin/reports/status to see the error which reads "For this to work correctly, all tables must have a primary key. The following table(s) do not have a primary key: otp_settings, email_login_otp."

Proposed resolution

Add a primary key to those table definitions inside email_login_otp_schema() and write a hook_update_N() implementation to add those keys to existing installs.

Here is a patch which does this.
As far as I can tell from reading through the code the composite key of "uid,otp" should be unique.