chore(deps): bump github.com/bluekeyes/go-gitdiff from 0.8.1 to 0.9.0 - #220

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-go@v5, github/codeql-action/analyze@v3, github/codeql-action/init@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/