[zlib] Suppress MSan reports in chunkcopy operations

These operations are used to copy bytes from previous positions in the
output buffer/window, but since the chunks are wide they may overlap
with parts of the buffer that haven't been written yet. MSan would
report this under certain circumstances (see bug), but since the bytes
will not be used, suppress the reports.

Bug: 1376033, b/253633142
Change-Id: I73f3174fb347618b4080cfc8a042082473960582
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3963188


Auto-Submit: Hans Wennborg <hans@chromium.org>
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1061190}
NOKEYCHECK=True
GitOrigin-RevId: dbb556776f9a6d2c7464cd614f8d5863abade488