Add specs for CI runner minutes report email

What does this MR do and why?

This MR follows up on #435597 to add specs for CI runner minutes report email and confirm that an attachment is present. It removes a similar test from the Notify class, where the module is included.

EE: true

Closes #435597

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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MR acceptance checklist

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