`ffmpeg.wasm-core` fails to build in docker

**Describe the bug**
Fresh checkout of `ffmpeg.wasm-core` on main branch `n4.3.1-wasm` fails to build using `bash ./build-with-docker.sh`

**To Reproduce**
```sh
git clone git@github.com:ffmpegwasm/ffmpeg.wasm-core.git
cd ffmpeg.wasm-core
bash ./build-with-docker.sh
```

Error is:
```
CMake Error: The source directory "/src/third_party/zlib" does not appear to contain CMakeLists.txt.
```