contrib/gfx: Fix steam game information retrieving script

Fix user agent string in request header in
contrib/gfx/steam_game_info.py script

BUG=b:196916787
TEST=Tested locally

Change-Id: I7ae25692d4b54feceee1d4759f3db59363120e4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/3098601
Reviewed-by: Po-Hsien Wang <pwang@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Commit-Queue: Ilja H. Friedel <ihf@chromium.org>
Tested-by: Ilja H. Friedel <ihf@chromium.org>
1 file changed