Update feature specs for vue_issues_list (part 2)

What does this MR do and why?

The vue_issues_list feature flag is now default enabled in the code, for the refactor of the group/project issues page to Vue (#322755 (closed)).

The feature specs were updated with this feature flag enabled in !61123 (closed) but it has a large diff so it is being split into several MRs to make reviewing easier.

Once all the MRs have been merged, a final MR will be created to remove all stub_feature_flags(vue_issues_list: true) lines of code.

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