Bump third_party/nanopb/repo from `5fd8f04` to `423c03b` #1242

Job	Run time
Build on Darwin (clang, python_lib, simulated)	1h 4m 53s
Build on Linux (fake, gcc_release, clang, simulated)	1h 24m 3s
Build on Linux (coverage)	1h 46m 23s
Build on Linux (python_lib)	18m 42s
Build on Linux (python lighting-app)	2h 7m 30s
Build on Linux (gcc_debug)	55m 48s
	7h 37m 19s

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