Fixes package tag not being displayed

What does this MR do and why?

When tag count is 1, adds important flag to gl-flex class in package-tags component.

This used to be gl-display-none and was changed to gl-flex in !163424 (diffs)

This probably caused a specificity change which is why we need to add the important flag.

Changelog: fixed

Fixes #496602 (closed)

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Get the project id.
2. In rails console, run the following:

def fixture_file_upload(*args, **kwargs)
  Rack::Test::UploadedFile.new(*args, **kwargs)
end

project = Project.find(<id>) 

package = FactoryBot.create(:npm_package, project: project)

FactoryBot.create(:packages_tag, package: package, name: 'latest')

FactoryBot.create(:npm_package, project: project).tap { |pkg| 2.times.each { |i| FactoryBot.create(:packages_tag, package: pkg, name: "bananas_#{i}") } }

FactoryBot.create(:npm_package, project: project).tap { |pkg| 3.times.each { |i| FactoryBot.create(:packages_tag, package: pkg, name: "bananas_#{i}") } }

3. Visit Project > Deploy > Package Registry & the confirm labels are displayed for packages with just one tag