tests: Add test scenario for GC9A01 display controller.

[nedseb]

Add a YAML test scenario file tests/scenarios/gc9a01.yaml for the GC9A01 driver.

Expected tests

• Mock: verify initialization sequence
• Hardware: basic display operations (fill, text)
• Manual: validate display output visually

Reference

• Driver: lib/gc9a01/
• Test framework: PR tests: add test framework with mock and hardware support. #28

Blocked by

• gc9a01: Add GC9A01 round color display driver #10 — Driver must be implemented first.