https://tools.wmflabs.org/osmlint/: https://camo.githubusercontent.com/365986a132ccd6a44c23a9169022c0b5c890c387/68747470733a2f2f73332e616d617a6f6e6177732e636f6d2f6769746875622f726962626f6e732f666f726b6d655f72696768745f7265645f6161303030302e706e67

Loading from external providers are discouraged. Please see parent tasks and J65.
In your case possible solutions would be:

• Use https://simonwhitaker.github.io/github-fork-ribbon-css/, we provide the css on https://tools-static.wmflabs.org/cdnjs/ajax/libs/github-fork-ribbon-css/
• https://tools.wmflabs.org/static-browser/ may have provided this image, but the service may be down at the moment
• Host the image file in your tool