Fix broken link in upgrade-nap-waf.md

[nginx-aoife]

Fix broken link in nginx-app-protect-waf

Proposed changes

Problem: Automation found broken link in nginx-app-protect-waf docs. https://github.com/nginx/documentation/actions/runs/12685140469/job/35354980039
Possibly caused by Azure content update.

Solution: URL is updated.

Testing: Local testing, URL opens correctly. No more 404

Checklist

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• I have read the contributing guidelines

• I have signed the F5 Contributor License Agreement (CLA)

• If applicable, I have added tests that prove my fix is effective or that my feature works

• If applicable, I have checked that any relevant tests pass after adding my changes

• I have updated any relevant documentation (README.md and CHANGELOG.md)

• I have rebased my branch onto main

• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

• If the change involves:

  • Code
  • Anything that resembles Personally identifying information (PII)
    • Make sure to use placeholders such as <username> in place of PII
  • URLs (watch for typosquatting)
  • Significant new/revised content

  In these cases, the change will require at least two (2) approvals before merging

[github-actions]

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[github-actions]

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[nginx-aoife]

I have hereby read the F5 CLA and agree to its terms

[ADubhlaoich]

LGTM though I have added an edit suggestion to use a Hugo reference.

These are docsets living together in the same codebase, so it doesn't make much sense to use a live URL to link between documents.