Update copyright headers in third_party/zlib/

This is forked and this repo is authoritative for the fork.

The methodology used to generate this CL is documented in
https://crbug.com/1098010#c95.

No-Try: true
Bug: 1098010
Change-Id: I4698084a28dda86210e9dba6ddac76c13377e687
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3921823


Auto-Submit: Avi Drissman <avi@chromium.org>
Reviewed-by: Adam Langley <agl@chromium.org>
Commit-Queue: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1051972}
NOKEYCHECK=True
GitOrigin-RevId: 9fc44ce454cc889b603900ccd14b7024ea2c284c