fix icebreaker link

[avallecam]

if the expected behaviour is that the link within these two callouts works the same:

• https://carpentries.github.io/lesson-development-training/aio.html#before-the-training-begins
• https://carpentries.github.io/instructor-training/01-welcome.html#before-the-course-begins

then, the link could be redirected to https://carpentries.github.io/instructor-training/icebreakers.html

[github-actions[bot]]

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