Bump third_party/openthread/repo from `66eaeec` to `f239c49` #1109

Job	Run time
REPL Tests - Linux	28m 1s
Test Suites - Darwin (no-ble-asan-clang)	1h 14m 21s
Test Suites - Linux (no-ble-tsan-clang)	1h 20m 43s
Test Suites - Darwin (no-ble-tsan-clang)	1h 59m 48s
REPL Tests - Darwin	0s
	5h 2m 53s

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