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

Job	Run time
Unit / Integration Tests (main)	6m 12s
Unit / Integration Tests (clang)	6m 17s
Unit / Integration Tests (mbedtls)	5m 41s
Unit / Integration Tests (rotating_device_id)	6m 18s
	24m 28s

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