Bump third_party/pigweed/repo from `ce0e3e2` to `b8d1cd0` #991

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	56m 33s
Build on Linux (gcc_debug)	1h 7m 39s
Build on Linux (python_lib)	23m 30s
Build on Linux (python lighting-app)	5m 57s
Build on Linux (coverage)	12m 40s
Build on Darwin (clang, simulated)	1h 9m 48s
	3h 56m 7s

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