Sort by PR number

[timja]

Mostly addresses #476 (comment)
It doesn't work for e.g. 10 which is sorted before 2, but this should restore the previous sort order.

Example PRs:

Branches layout is fine:

FYI @janfaracik

Testing done

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• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[jtnord]

I think so. If someone selected a non default display option, this could cause some confusion, but the sort order would be consistent and not depend on the display option