E2E test: return if namespace is filled in

What does this MR do and why?

Resolves #420844 (closed)

The above failure occurs because when we search for a namespace, a result is not displayed since the namespace is already selected by default.

When creating a project from a template from a group, the group is the default namespace on the dropdown page. This MR will change the test so it will only choose a value from the dropdown if it isn't already selected. This should slightly speed up the test and make it more reliable.

I have verified this fix in staging also.

How to set up and validate locally

QA_LOG_LEVEL=DEBUG QA_GITLAB_URL=http://192.168.4.31:3000  bundle exec rspec qa/specs/features/ee/browser_ui/3_create/repository/project_templates_spec.rb

QA_GITLAB_URL=https://staging.gitlab.com bundle exec rspec qa/specs/features/ee/browser_ui/3_create/repository/project_templates_spec.rb

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