Add .proto ext to check-license-header.sh #63

Job	Run time
Soundness / Unacceptable language check	5s
Soundness / Documentation check	39s
Soundness / License headers check	5s
Soundness / API breakage check	0s
Soundness / Broken symlinks check	4s
Soundness / Format check	0s
Soundness / Python lint check	7s
Soundness / Shell check	32s
Soundness / YAML lint check	4s
	1m 36s

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