Update header image

[johndcoy]

Updates the WPORG plugin header.

Changes proposed in this Pull Request:

This PR updates the plugin header to reflect the new Stripe banner.

Testing instructions

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• Covered with tests (or have a good reason not to test in description ☝️)
• Added changelog entry in both changelog.txt and readme.txt (or does not apply)
• Tested on mobile (or does not apply)

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)