Bump third_party/openthread/repo from `66eaeec` to `f239c49` #1108

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	28m 38s
Test Suites - Darwin (no-ble-asan-clang)	1h 22m 50s
Test Suites - Darwin (no-ble-tsan-clang)	1h 52m 48s
Test Suites - Linux (no-ble-tsan-clang)	1h 32m 32s
	5h 16m 48s

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