Bump third_party/pigweed/repo from `9e4bfb9` to `34a7853` #600

Job	Run time
Unit / Integration Tests (main)	5m 22s
Unit / Integration Tests (clang)	4m 51s
Unit / Integration Tests (mbedtls)	1m 0s
Unit / Integration Tests (rotating_device_id)	56s
	12m 9s

Provide feedback