Fix the broken commit hash tag of the 'FST-matlab-struct-utilities' submodule
The current hash tag isn't resolveable anymore therefore hindering efficient recursive cloning of the repository.
You can test this by clicking on the commit hash tag hyperlink of the submodule in the repository overview in GitLab (it currently displays @b59a2e43). This happens after force pushing commits (overwriting them), referencing a commit on a branch that gets deleted by squash pushing to a different branch and deleting the source branch. Most probably something I messed up.
This merge request sets the 'fst-matlab-struct-utilities' submodule to a valid commit hash tag (the currently last one on the main branch, @ac62a61a)
Sebastian