fix: Webhook provider uses dummy payload for validation

[yosizelensky]

Closes #5319

📑 Description

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

[vercel]

@yosizelensky is attempting to deploy a commit to the KeepHQ Team on Vercel.

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[CLAassistant]

All committers have signed the CLA.

[shahargl]

lgtm

[vercel]

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
keep	Ignored	Preview		Sep 21, 2025 10:58am

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.45%. Comparing base (57ca737) to head (f3fc2ea).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5320      +/-   ##
==========================================
- Coverage   46.64%   46.45%   -0.19%     
==========================================
  Files         175      176       +1     
  Lines       18263    18385     +122     
==========================================
+ Hits         8519     8541      +22     
- Misses       9744     9844     +100     

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[shahargl]

Lgtm

[github-actions]

🚀 Fantastic work @yosizelensky! Your very first PR to keep has been merged! 🎉🥳

You've just taken your first step into open-source, and we couldn't be happier to have you onboard. 🙌
If you're feeling adventurous, why not dive into another issue and keep contributing? The community would love to see more from you! 🚀

For any support, feel free to reach out on the community: https://slack.keephq.dev. Happy coding! 👩‍💻👨‍💻