ci(genai): Update `genai` directory to run tests in specific directories only #1236

Job	Run time
region tags	10s
(legacy) Finding affected tests	13s
lint	41s
(legacy) test (genai/tuning)	27s
(legacy) test (genai/content-cache)	31s
(legacy) test (genai/controlled-generation)	44s
(legacy) test (genai/tools)	59s
(legacy) test (genai/count-tokens)	37s
(legacy) test (genai/bounding-box)	43s
(legacy) test (genai/text-generation)	3m 5s
(legacy) test (genai/thinking)	54s
(legacy) test (genai/image-generation)	1m 10s
(legacy) test (genai/live)	39s
	10m 53s

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