Resolve ESLint violations in React Native test fixtures

[twometresteve]

Goal

Resolves several ESLint violations in the React Native test fixtures.

Design

Apologies for the slightly unwieldy PR - it was very easy to produce with the help of an ESLint literate IDE!

Changeset

The most important aspects of the PR are:

• The updated ignore file, which brings the React Native test folder into scope (but not other test folders at this stage). This ensures that npm run test:lint catches violations when run locally.
• Addition of test to Dockerfile.ci, ensuring that the files are in scope for Linting in CI.

Testing

In addition to passing CI:

• Verified that npm run test:lint gives a clean result locally (and detects the deliberate introduction of a violation in the RN test fixtures).
• Verified that errors will be caught on CI (this was initially missed when working the branch and hence the change to Dockerfile.ci.

[bugsnagbot]

@bugsnag/browser bundle size diff

	Minified	Minfied + Gzipped
Before	40.57 kB	12.52 kB
After	40.57 kB	12.52 kB
±	No change	No change

Generated by 🚫 dangerJS against b7fa1a1

[djskinner]

👍