Bump submodule/zlib from ac8f12c to 643e17b (bruderstein#200)

Bumps [submodule/zlib](https://github.com/madler/zlib) from `ac8f12c` to `643e17b`.
- [Release notes](https://github.com/madler/zlib/releases)
- [Commits](madler/zlib@ac8f12c...643e17b)

---
updated-dependencies:
- dependency-name: submodule/zlib
  dependency-type: direct:production
...

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