Notifications for CI Minutes quota limits should not mention purchases for self-hosted GitLab

Summary

Self-hosted GitLab users receive a notification email of the sort below:

This is an automated notification to let you know that your CI Runner Minutes quota for "example.com" is below 5%.

Click here to purchase more minutes.

If you need assistance, please contact GitLab support.

The "Click here to purchase more minutes" text caused a premium customer to misunderstand (Zendesk, internal only) that we were asking them to make an additional purchase.

Steps to reproduce

Set up a pipeline minutes quota for your instance.

What is the current bug behavior?

The text says to purchase more minutes - this is a SaaS feature. We do not currently offer add-on shared runner minutes for self-managed instances.

What is the expected correct behavior?

• Self-managed users should not receive email notifications
• Self-managed users should receive the following in-app notifications:

1. When quota has expired: Your pipelines quota has expired, please contact your systems administrator
2. At 10% of quota left: Your pipelines quota is about to expire, please contact your systems administrator

Relevant logs and/or screenshots

(Paste any relevant logs - please use code blocks (```) to format console output, logs, and code as it's tough to read otherwise.)

Output of checks

Reported in 12.1.0-ee

Possible fixes

This was introduced in https://gitlab.com/gitlab-org/gitlab-ee/commit/8d8e2098dde7c9f21ba51e8b033b46a13ce467a6.

I think we're just missing some if ::Gitlab.com? conditionals.