Centerize text on Mark all as done button on To-Do List

What does this MR do?

Centerizes text on Mark all as done button on To-Do List. Addresses the regression from !25142 (merged) (%12.9).

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [n/a] Documentation (if required)
• Code review guidelines
• [n/a] Merge request performance guidelines
• Style guides
• [n/a] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #244844 (closed)