Fix webhook secret file names

[jhrozek]

Summary

Here's what happened:

• I submitted PR Use webhook secrets from files #3177
• Ria submitted feedback inline, I accepted it. The suggestions were
  merged into the remote branch.
• the patch had conflicts with main
• I resolved the conflicts locally and force-pushed to the remote branch. My
  local branch didn't have Ria's suggestions and the force-push removed
  them

This patch brings back Ria's suggestions so I included her as a
co-author.

Sorry!

Co-authored-by: Eleftheria Stein-Kousathana eleftheria@stacklok.com

Change Type

• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Just visually.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[JAORMX]

oops!

[coveralls]

coverage: 50.523%. remained the same
when pulling e94c7f4 on jhrozek:use_wh_secret_from_file
into 0f68185 on stacklok:main.