Revert 324246-fix-incorrect-trigger-property-name

What does this MR do?

<gl-popover> accepts a triggers prop to control how the popover is shown. One component was using trigger="manual", which is incorrect and wasn't doing anything. In a previous MR I changed it to triggers="manual". However, it breaks a Ruby test that expects the incorrect behavior: https://gitlab.com/gitlab-org/gitlab/-/jobs/1145163252. This MR reverts that change to re-break the manual trigger, but lets the test pass.

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