Repeated fields arent allowed outside of attribution node and key value
pairs, so we should fail to build if someone attempts to add one.
Bug: 149956370
Test: atest stats-log-api-gen-test
Change-Id: I0caa6fcf74dabe8e962360ecccfd3a87fcaa4909
Merged-In: I0caa6fcf74dabe8e962360ecccfd3a87fcaa4909