Bump third_party/pigweed/repo from `9504c03` to `1dc8cfc` #1086

Job	Run time
Build on Darwin (clang, python_lib, simulated)	4m 12s
Build on Linux (coverage)	7m 16s
Build on Linux (fake, gcc_release, clang, simulated)	5m 13s
Build on Linux (gcc_debug)	7m 27s
Build on Linux (python_lib)	7m 14s
Build on Linux (python lighting-app)	4m 1s
	35m 23s

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