chore: fix kokoro with safedir for git

[quartzmo]

Fixes kokoro error:

+ git clone . /root/go/src/google.golang.org/genproto
Cloning into '/root/go/src/google.golang.org/genproto'...
fatal: detected dubious ownership in repository at '/tmpfs/src/github/go-genproto/./.git'
To add an exception for this directory, call:

	git config --global --add safe.directory /tmpfs/src/github/go-genproto/./.git
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.