Bump third_party/nanopb/repo from `5fd8f04` to `cf26d28` #1238

Job	Run time
Build on Darwin (clang, python_lib, simulated)	1h 14m 53s
Build on Linux (fake, gcc_release, clang, simulated)	1h 24m 52s
Build on Linux (coverage)	9m 52s
Build on Linux (gcc_debug)	45m 28s
Build on Linux (python_lib)	19m 3s
Build on Linux (python lighting-app)	9m 45s
	4h 3m 53s

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