ci : add apt-get clean to musa Dockerfile (#3275)

ci : add apt-get clean to musa Dockerfile (#3275)

* ci : add apt-get clean to musa Dockerfile

This commit adds `apt-get clean` to the musa Dockerfile to reduce the
image size by removing cached package files after installation.

The motivation for this is to try to reduce the size of the Docker image
and see if this can avoid the "no space left on device" error during
the CI build process.

Refs: https://github.com/ggml-org/whisper.cpp/actions/runs/15815324254