breaking GitHub Actions' workflow builds. These builds were working with the 4.0.12 Docker image.

Here is the output from ls -l run in Docker.

-rwxr--r-- 1 emscripten emscripten 1008 Aug 14 19:24 /emsdk/upstream/emscripten/embuilder

Why is this a problem?

When using the docker image in a GHA workflow and you start Docker with

docker run -dit --name emscripten -v $(pwd):/src emscripten/emsdk bash

/src ends up being owned by the uid/gid of the user that launched the workflow and commands are executed by that same user who cannot execute embuilder: Permission denied.*

Note that if you use the same command on you local machine /src is owned by and commands are run by root so no problem.

* On GitHub you actually need to use the command

docker run -dit --name emscripten --user "$(id -u):$(id -g)" -v $(pwd):/src emscripten/emsdk bash

to run docker so the user becomes the user who owns the repo in the workflow because of a security fix in Git that disallows Git commands not run by the repo owner.