GitHub now allows adding a donate button on top of your repository via a FUNDING.yml file. While I wouldn't expect a huge effect, maybe worth adding to the Wikimedia repos and pointing it to the Wikimedia donation page.
(What exactly should count as a "Wikimedia repo" is debatable. Just because some extension or library is deployed in production, we shouldn't prevent the author from running their own personal fundraising campaign if they want. But extensions / libraries predominantly created by WMF staff in paid time should be fair game. Probably MediaWiki too, although that should probably be discussed within the developer community first.)