Bump third_party/pigweed/repo from `1f12d06` to `39dbc59` #970

Job	Run time
Build on Darwin (clang, python_lib, simulated)	2m 33s
Build on Linux (fake, gcc_release, clang, simulated)	30m 18s
Build on Linux (coverage)	15m 18s
Build on Linux (gcc_debug)	1h 5m 25s
Build on Linux (python_lib)	3m 5s
Build on Linux (python lighting-app)	3m 28s
	2h 0m 7s

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