Fix `undefined` tooltip for `Toggle commit description` button

What does this MR do and why?

Contributes to #429317 (closed)

Problem

After first click on Toggle commit description the tooltip displays undefined text.

Solution

Define collapse-title and expand-title to fix the problem.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a commit with a description
2. Find the commit in any of the overviews
3. Press the "Toggle commit description" button
4. See that the text is changed to "undefined"

Example project: https://gitlab.com/DaanHaitsma/undefined/-/blob/main/README.md

MR acceptance checklist

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