Update release instructions to include merge verification

[jeffpaul]

Added a step to verify the merge from develop to trunk.

What?

This pull request makes a small update to the release instructions documentation by adding an additional verification step after merging branches.

• Added a step to compare develop and trunk branches after merging, ensuring no results show in the comparison to confirm the prior steps completed successfully.

Why?

This is a manual check I do that isn't properly captured in the release instructions, so this PR adds that in.

How?

Use of AI Tools

Testing Instructions

Testing Instructions for Keyboard

Screenshots or screencast

Before	After

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[dkotter]

Thinking about this some more, I think what happened here is the release PR was merged into develop and then develop was merged into trunk but the latest changes in develop weren't pulled down first.

If we want, we can make these instructions a bit more specific to make that clear (something we changed in the release instructions for our plugins).

Suggested change

	- [ ] Merge release PR: Make a non-fast-forward merge from your release branch to `develop` (or merge the pull request).
	- [ ] Merge develop to trunk: Do the same for `develop` into `trunk` (`git checkout trunk && git merge --no-ff develop`). `trunk` now contains the stable development version.
	- [ ] Merge release PR: Make a non-fast-forward merge from your release branch to `develop` (or merge the pull request).
	- [ ] Merge develop to trunk: Do the same for `develop` into `trunk`, ensuring you pull the most recent changes into `develop` first (`git checkout develop && git pull origin develop && git checkout trunk && git pull origin trunk && git merge --no-ff develop`). `trunk` now contains the stable development version.

[jeffpaul]

Updated in #291.