tools: Fix bug in check-changelogger-use debug

[anomiex]

Proposed changes:

When #36593 added a $fmt arg, it didn't update the code correctly.

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Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• Run it with --debug, or just check the log output for the CI run on this PR.
  • https://github.com/Automattic/jetpack/actions/runs/13379545995/job/37365550490?pr=41858#step:5:12

[github-actions]

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[tbradsha]

In current trunk:

$ tools/check-changelogger-use.php --debug trunk trunk
trunk

In this branch:

$ tools/check-changelogger-use.php --debug trunk trunk
Checking diff from trunk...trunk.