Remove changelog checks for branches other than trunk

[ellatrix]

What?

We shouldn't run these tests for branches such as #62641.

Why?

It will try to match the wrong PR (this one).

How?

Testing Instructions

Confirm the tests run here, confirm they are gone in #62641.

Testing Instructions for Keyboard

Screenshots or screencast

[github-actions]

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[github-actions]

Flaky tests detected in 56a3c23.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/9561419812
📝 Reported issues:

• [Flaky Test] Redirection after template creation #60678 in /test/e2e/specs/site-editor/site-editor-url-navigation.spec.js