[zlib] Update zlib headers in GN

This will ensure changes to the headers force rebuilds of each
zlib source set target. This was picked up by a tool in ANGLE
(i.e. scripts/export_targets.py).

Bug: 1032721
Change-Id: Id64d02e1a11faefce2a88fb740e9bf1db32763dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2383291


Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803698}
GitOrigin-RevId: d40bde4a68f7c98168286b19d8c4e5fa27e33e2c