[Markdown] add more tests to Markdown

[ConeDragon]

edit:
make sure _ and __ don't get interpreted

possible suggestion:
maybe add two matching opening/closings throughout 2 paragraphs that should not be interpreted

[github-actions]

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[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

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[no important files changed]

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