Danger bot: Apply test label for files related to feature specs

What does this MR do?

Update Danger bot rules to apply the test label for files related to feature specs (shared_examples, shared_contexts, helpers). The intention is to make the labelling consistent with feature specs, which are also labelled as test.

Example

Before

[24] pry(main)> categories_for_file('spec/support/shared_examples/features/master_manages_access_requests_shared_example.rb')
=> [:backend]

After

[28] pry(main)> categories_for_file('spec/support/shared_examples/features/master_manages_access_requests_shared_example.rb')
=> [:test]

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done