Fixed LaTeX rendering in some demo notebooks

[ZiadAmerr]

The current notebooks are incorrectly rendered because the dollar sign should not be perceded by a space to be rendered correctly in Visual Studio Code cells, adding a space around them fixes the problem, however it does render correctly on GitHub.

The part in red is the default format, the part in green is the fixed format.

[github-actions[bot]]

:point_left: Launch a Binder on branch ZiadAmerr/nbgrader/main

[brichet]

Thanks @ZiadAmerr. Can you rebase on main please, to make sure the tests pass ?

[ZiadAmerr]

You're welcome @brichet :)