Bump deps/zstd from 8689633 to 20707e3

Bumps [deps/zstd](https://github.com/facebook/zstd) from `8689633` to `20707e3`.
- [Release notes](https://github.com/facebook/zstd/releases)
- [Commits](facebook/zstd@8689633...20707e3)

---
updated-dependencies:
- dependency-name: deps/zstd
  dependency-type: direct:production
...

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