add weekly tests for both octave and matlab

[chrishavlin]

Would be good to add a weekly test in github actions.

More info:

• Existing github workflows are stored in https://github.com/vbr-calc/vbr/tree/main/.github/workflows . Easiest thing to do is copy the 2 build-test-matlab.yml and build-test-octave.yml workflows into 2 new files and change the trigger (on:) to run on a schedule
• github docs on schedule parameter for github actions
• example weekly test from yt_xarray