CMake: Resolve Missing ZLIB Warning When PNG is Disabled (backport #3054)

[mergify]

closes #3053

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This is an automatic backport of pull request #3054 done by Mergify.

[mergify]

Cherry-pick of 81bc63d has failed:

On branch mergify/bp/0.28.x/pr-3054
Your branch is up to date with 'origin/0.28.x'.

You are currently cherry-picking commit 81bc63d9c.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/CMakeLists.txt

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally