Investigate musllinux-arm64 CI test hangs for Python 3.9, 3.10, 3.11

Description

In the linux-test CI matrix added in grafana/pyroscope-rs#364, the musllinux-arm64 variant hangs indefinitely for Python 3.9, 3.10, and 3.11, while 3.12 and 3.13 complete successfully (~37s each).

All four variants started at the same time. The three older versions never complete.

Observed behaviour

Example run: https://github.com/grafana/pyroscope-rs/actions/runs/22293868489

Possible causes

• python:3.9-alpine, python:3.10-alpine, python:3.11-alpine images may not have an arm64 variant on Docker Hub, causing docker pull to hang or fail silently
• py-spy may not support profiling on Alpine arm64 for older Python versions
• The test watchdog (120s timeout) fires but the process doesn't exit cleanly inside the container

Current workaround

These three combinations are excluded from the matrix via exclude: in ci-ffi-python.yml until the root cause is identified.

Next steps

• Check Docker Hub for python:3.9-alpine / 3.10-alpine / 3.11-alpine arm64 manifest availability
• Run the docker pull manually on an arm64 runner to confirm
• Check if py-spy works on Alpine arm64 for these Python versions

Start with ci-ffi-python.yml and the linked Actions run, then check Docker Hub manifests for the Python 3.9–3.11 Alpine arm64 images. Reproduce the pulls and py-spy test on an arm64 runner, checking the 120-second watchdog behavior. Done means the hang’s cause is identified and the exclusion or CI configuration can be updated accordingly.