Bump third_party/openthread/repo from `2aeb8b8` to `ff19e03` #399

Job	Run time
REPL Tests - Linux	1h 34m 34s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 39m 39s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	2h 3m 50s
Test Suites - Linux (no-ble-no-shell-tsan-clang)	2h 0m 59s
REPL Tests - Darwin	0s
	7h 19m 2s

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