Run infection scanner specs when its config changes

What does this MR do and why?

The vitest suite under spec/frontend/scripts/infection_scanner/ covers the bundler-side infection helpers as well as the scanner itself. vue3_infection_shared_spec.mjs tests createIsInfectable, which lives in config/helpers/vue3_infection_shared.js.

But .frontend:rules:test-infection-scanner only listed the scanner and spec directories in its changes:. A change to createIsInfectable or to the context aliases got a green pipeline that never ran the specs written for it.

This adds the six infection-related config files to that list.

How to verify

1. Check that the test-infection-scanner job appears on this pipeline. It should not, because this MR touches no path in the list.
2. On a follow-up MR that edits config/helpers/vue3_infection_shared.js, confirm the job now appears.

No changelog entry: this is CI configuration with no user-facing effect.

References

• Found while fixing #625296 (closed), whose fix edits config/helpers/ and would otherwise have merged without its own specs running
• Analysis of the underlying defect: #625296 (comment 3760799545)