Bump third_party/openthread/repo from `2aeb8b8` to `f6cee79` #6067

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	1h 34m 1s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 33m 59s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 50m 21s
Test Suites - Linux (no-ble-no-shell-tsan-clang)	2h 0m 44s
	6h 59m 5s

Provide feedback