ci(release): update mf6 to 6.8.2 and gridgen to v1.0.03 - #80

The run was canceled by @wpbonelli.

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/upload-artifact@v4, nick-fields/retry@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/