DKIM, DMARC, SPF, etc., all pass, so the email seems legitimate. I'm not sure why their staging environment is sending out real emails to customers.
Title: [STAGING Cloudflare] Billing Account Email Changed
From: [email protected]
Hello,
You will no longer receive Cloudflare billing
notifications to this email address because your
Cloudflare account billing email has been updated.
Log in to view and modify your billing email address on
file. Please allow up to 15 minutes for the billing email
to update on the dashboard.
For additional assistance, refer to our Support portal.
Thanks,
The Cloudflare Team