Colab badge pointing to wrong from previous release

[jcohenadad]

When attempting to run the notebook in colab from a previous release: https://github.com/shimming-toolbox/rf-shimming-7t/tree/r20240213?tab=readme-ov-file

clicking on the link brings to the 'main' branch, and since the notebook file name has changed, the link is not working anymore. The badge should have pointed to the release branch (which was not created before creating the release, so that's a chicken and egg problem)