util/lint: Add .gitignore files to list that don't need a license

Signed-off-by: Martin Roth <martin.roth@amd.corp-partner.google.com>
Change-Id: I568a357b40e8bb69b2b26752d241f06adfbe029e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66503
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>

util/lint/lint-000-license-headers

@@ -34,6 +34,7 @@ EXAMPLE|\
 NEWS|\
 ChangeLog|\
 Dockerfile|\
+\.gitignore$|\
 \.in$|\
 \.[18]$|\
 \.md$|\