Bump third_party/pigweed/repo from `1f12d06` to `1247e8d` #2328

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	1h 43m 0s
Build on Linux (gcc_debug)	1h 13m 33s
Build on Linux (python_lib)	1m 50s
Build on Darwin (clang, python_lib, simulated)	3m 8s
Build on Linux (coverage)	16m 49s
Build on Linux (python lighting-app)	1m 46s
	3h 20m 6s

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