Fix flaky ./ee/spec/features/projects/packages_spec.rb:177

Fix occasional capybara Ambiguous matches. There were sometimes multiple trs passed to page.within, and instead pass it the whole table.

There is still a race condition due to visiting the page before we create the data in packages_spec, but this should prevent the duplicate row selector error of #211142 (closed)

Fixes #211142 (closed)