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

| Job | Status | Duration |
|-----|--------|----------|
| musllinux-arm64 - 3.9 | stuck in_progress | 15+ min |
| musllinux-arm64 - 3.10 | stuck in_progress | 15+ min |
| musllinux-arm64 - 3.11 | stuck in_progress | 15+ min |
| musllinux-arm64 - 3.12 | completed | ~37s |
| musllinux-arm64 - 3.13 | completed | ~37s |

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.

索引モデルが issue の本文から書いたものです。