Update test_fonts git ignore for GCS

Updates the git ignore file in separate CL, so that if test_fonts gcs CL is reverted, files will not be left on users' systems.

Migration CL (https://chromium-review.googlesource.com/c/chromium/src/+/5491359)

Bug: 336625018
Change-Id: I0825a5d3197c465ccd15fc93756504a91ee331ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5490641
Commit-Queue: Benjamin Joyce (Ben) <bjoyce@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1292638}
NOKEYCHECK=True
GitOrigin-RevId: b59f065ada899d33ef156c920489abadc2b4577c