Bump third_party/pigweed/repo from `9e4bfb9` to `3623b95` #713

Job	Run time
Build on Darwin (clang, python_lib, simulated)	4m 7s
Build on Linux (fake, gcc_release, clang, simulated)	6m 8s
Build on Linux (gcc_debug)	5m 38s
Build on Linux (python_lib)	4m 40s
Build on Linux (coverage)	3m 3s
	23m 36s

Provide feedback