[8.14] Update 8.15 changelog diff link (backport #13680)

[mergify]

Motivation/summary

Update link as 8.14.3 is released

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

Related issues

---

This is an automatic backport of pull request #13680 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 8a161ef has failed:

On branch mergify/bp/8.14/pr-13680
Your branch is up to date with 'origin/8.14'.

You are currently cherry-picking commit 8a161ef87.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   changelogs/8.15.asciidoc

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[carsonip]

It was a mistake. There is no need to backport 8.15 changelog to 8.14.