Bump third_party/libwebsockets/repo from `cfa9d88` to `1239a2b` #387

Job	Run time
Unit / Integration Tests (main)	13m 39s
Unit / Integration Tests (clang)	12m 52s
Unit / Integration Tests (mbedtls)	13m 3s
Unit / Integration Tests (rotating_device_id)	13m 44s
Unit / Integration Tests (icd)	43m 47s
	1h 37m 5s

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