Fix up invalid github URLs

[clrudolphi]

🤔 What's changed?

Changed the URLs in a few error messages that would lead users to a 404 on the Github.com website. The corrections lead them now to https://reqnroll/Reqnoll.VisualStudio/issues

⚡️ What's your motivation?

Prevent user frustration.

🏷️ What kind of change is this?

• :bank: Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)

📋 Checklist:

None of these required, simple spelling issue.

• [ ] I've changed the behaviour of the code
  • [ ] I have added/updated tests to cover my changes.
• [ ] My change requires a change to the documentation.
  • [ ] I have updated the documentation accordingly.
• [ ] Users should know about my change
  • [ ] I have added an entry to the "[vNext]" section of the CHANGELOG, linking to this pull request & included my GitHub handle to the release contributors list.

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[ajeckmans]

Great changes. I do wonder whether we should not just include this in the changelog as well.

[Code-Grump]

Documentation is a feature as much as the software itself and contributions should be recognised, even if they're in a separate changelog.