Bump third_party/pigweed/repo from `9504c03` to `fbb318a` #1069

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	1h 56m 46s
Build on Linux (gcc_debug)	1h 5m 8s
Build on Linux (python_lib)	41m 15s
Build on Darwin (clang, python_lib, simulated)	57m 19s
Build on Linux (coverage)	14m 25s
Build on Linux (python lighting-app)	10m 21s
	5h 5m 14s

Provide feedback