[Backport 7.63.x] exclude `.git` from copyright linter #69456

Job	Run time
agenttelemetry-list-change-ack-check	40s
assign-team-label	35s
release-note-check	1m 1s
ask-reviews	0s
fetch-labels	2s
skip-qa-check	25s
team-label-check	1s
	2m 44s

Provide feedback