Bump third_party/openthread/repo from `f0b6fce` to `a147485` #905

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	1h 2m 50s
Test Suites - Darwin (no-ble-asan-clang)	1h 20m 17s
Test Suites - Darwin (no-ble-tsan-clang)	1h 49m 16s
Test Suites - Linux (no-ble-tsan-clang)	1h 35m 57s
	5h 48m 20s

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