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