Update collaboration-via-github session with new slides and workshop challenges

[PaoloBozzini]

• Restructure session plan into theory, scenario challenges, and hands-on workshop.
• Add git-workshop-challenges.zip with 6 interactive challenges.
• Update learning goals to include git workflows, tags, and bisect.

[adamblanchard]

Just a couple of things :)

Also, could i ask a favour, if you can run:
npm run generate:learning-goals Backend
npm run generate:learning-goals Frontend

It will copy the new learning goals into the course overview pages, so they stay in sync :) It may bring in some changes from other modules too, no worries (my bad, for not running it for a while if that's the case).

Thanks so much for contributing your learnings from teaching the module back into the program @PaoloBozzini 🙏 it's so appreciated to keep our content evolving and improving! 🙇

[PaoloBozzini]

Thanks @adamblanchard

Ran both commands:

• npm run generate:learning-goals Backend
• npm run generate:learning-goals Frontend

Changes are included in this PR. 😄