[backport] Fix issue label facet can overwrite selected labels

What does this MR do and why?

On global search page in sidebar filters for issues scope. The label filter can overwrite already selected filters.

Screenshots or screen recordings

Before	After
	after

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).

How to set up and validate locally

1. Make sure advanced search is installed and enabled
2. Visit search page http://gdk.test:3000/search?scope=issues&search=*
3. Filter by label in the left sidebar, apply
4. Search for additional label
5. Select one of the searched filters
6. Apply the filtered label

Related to #494659 (closed)