Enable 128k context for Gemma4-31B CUDA (#20316) #12396

Job	Run time
CI run decision / decide	30s
Get changed files / get-changed-files	2s
test-metal-backend-modules	0s
export-model-metal-artifact	0s
test-metal-qwen35-moe-tiny	0s
test-model-metal-e2e	0s
test-executorch-metal-build	0s
	32s

Provide feedback