CI: workaround for testsuite lockups with MATLAB R2024a

By symlinking ~/.MathWorks to /dev/null, MATLAB is unable to copy and launch
the ServiceHost binary, which seems to cause lockups. See for example:
https://git.dynare.org/Dynare/dynare/-/jobs/62558
https://git.dynare.org/Dynare/dynare/-/jobs/62547

(cherry picked from commit 18131492)