Resolve changing "from" version in diff comparison does not preserve "to" version

What does this MR do?

• Preserve selected versions when comparing changes in MR Changes tab

Why was this MR needed?

• The second select dropdown would always reset to master if the first select dropdown was set changed to latest version

Screenshots (if relevant)

When lastest version is selected and a comparison version other than master is already set, that version will remain set.

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #25836 (closed)