Bump version to 7.13.3

• Diff: https://gitlab.com/gitlab-org/gitlab-qa/-/compare/v7.13.2...3d8040998d7c2f8ee93e3699fbc4b2ea6d670cad

• Release notes:

### Fixes

- !787 Update CustomersDot staging URL

### Doc changes

- !731 Update remote grid docs and include mobile testing variables

• Checklist before merging:

  • Diff link is up-to-date.
  • Based on the diff, lib/gitlab/qa/version.rb is updated, according to SemVer.
  • Release notes are accurate.

• Checklist after merging:

  • Update the release notes for the newly created tag.