Prepare system notes spec for bv upgrade

What does this MR do?

This MR lays the groundwork for the BootstrapVue upgrade that will be done in this MR: !18913 (merged). Due to some changes in the BTooltip and BPopover components, some related tests started failing after the upgrade. Those tests need to be updated accordingly:

• Migrate specs to use vue-test-utils
• sync needs to be set to false
• attachToDocument must be true

This MR focuses on upgrading the tests located in spec/frontend/vue_shared/components/notes/system_note_spec.js.

Why are these changes necessary?

• The reason to migrate the tests to vue-test-utils is that it allows us to set the sync and attachToDocument properties.
• The reason to set attachDocument to true is that the BTooltip and BPopover directives expect to be attached to a document object.
• The reason to set sync to false is that otherwise, specs for components that use BTooltip or BPopover will fail with the following error:

TypeError: Cannot read property 'sync' of null