add proto3 flag to fix cargo doc generation #2627

Job	Run time
Checks (ubuntu-latest)	2m 35s
Tests (ubuntu-latest)	2m 53s
Checks (macos-latest)	2m 8s
Linux Integration (ubuntu-20.04, v1.6.36)	4m 6s
Tests (macos-latest)	2m 34s
Deny	50s
Linux Integration (ubuntu-20.04, v1.7.24)	3m 51s
Tests (windows-latest)	4m 51s
Linux Integration (ubuntu-20.04, v2.0.1)	4m 48s
Timings	1m 47s
Linux Integration (ubuntu-22.04, v1.6.36)	3m 38s
Windows Checks	5m 19s
Linux Integration (ubuntu-22.04, v1.7.24)	3m 58s
Windows Integration (windows-latest, 1.7.0)	4m 27s
Linux Integration (ubuntu-22.04, v2.0.1)	4m 24s
Report required job statuses	1s
	52m 10s

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