Drop dependabot as repo is inactive. - #330

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: krdlab/setup-haxe@23a78f711bc4a623db38eac90d351ff0027f0116. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/