Fix fibre port placed off the fibre axis in get_simulation_grating_fiber - #776

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: eWaterCycle/setup-apptainer@3f706d898c9db585b1d741b4692e66755f3a1b40. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/