Tests

Bump third_party/openthread/repo from `2aeb8b8` to `7886083` #6009

Job	Run time
REPL Tests - Linux	1h 31m 1s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 35m 35s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 49m 40s
Test Suites - Linux (no-ble-no-shell-tsan-clang)	1h 59m 0s
REPL Tests - Darwin	0s
	6h 55m 16s

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