docs: fix malformed link in SECURITY.md reporting instructions - #193

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: conforma/pr-size-label-action@8b1fcdb87ab3ef4b79f9708fedf686904375e2d3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/