Bump third_party/nanopb/repo from `5fd8f04` to `423c03b` #1053

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	46m 50s
Test Suites - Darwin (no-ble-asan-clang)	1h 27m 47s
Test Suites - Linux (no-ble-tsan-clang)	2h 59m 8s
Test Suites - Darwin (no-ble-tsan-clang)	3h 8m 59s
	8h 22m 44s

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