Update PI review EM guidance

John Hoperequested to merge
jh-clarify-calendar-month into main

The Dev PI Review is done monthly for the preceding calendar month. However, this continues to catch people out as they create MRs with moving-window updates (28 day) mid-month or attempt to update for the current month.

This small update adds to the guidance for EMs to ensure they're including the correct data, first-time.

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