Make isTmuxAvailable work on github actions #5316

Job	Run time
build-and-check	2m 42s
test-cli	1m 14s
test-packages/internal	47s
test-packages/agent-runtime	57s
test-packages/billing	40s
test-integration-.agents	46s
test-integration-packages/billing	43s
test-integration-common	40s
test-integration-packages/internal	34s
test-common	43s
test-integration-web	42s
test-.agents	34s
test-integration-packages/agent-runtime	41s
test-sdk	44s
test-web	44s
test-integration-sdk	40s
test-integration-cli	1m 1s
	14m 52s

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