Changed the update button the for bulk edit of mrs and issues

What does this MR do and why?

When bulk editing issues, MRs, or epics, the button to apply the changes said Update all, which is misleading since not all issues, or MRs, are going to be updated.

This MR fixes that by changing the button to instead say Update selected 🙂

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to any project's issues page (same for the MRs page and epics page)
2. Click the Bulk edit button at the top right corner
3. The primary button will show Update all on master and Update selected on this branch