Add Alpine to CI

[A5rocks]

Ref: https://github.com/python-trio/trio/issues/2885

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7cb15ea) 99.64% compared to head (b5a8e1c) 99.64%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2933 +/- ## ======================================= Coverage 99.64% 99.64% ======================================= Files 116 116 Lines 17506 17506 Branches 3148 3148 ======================================= Hits 17444 17444 Misses 43 43 Partials 19 19 ``` | [Files](https://app.codecov.io/gh/python-trio/trio/pull/2933?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=python-trio) | Coverage Δ | | |---|---|---| | [src/trio/\_tests/test\_socket.py](https://app.codecov.io/gh/python-trio/trio/pull/2933?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=python-trio#diff-c3JjL3RyaW8vX3Rlc3RzL3Rlc3Rfc29ja2V0LnB5) | `100.00% <100.00%> (ø)` | |

[A5rocks]

Doesn't look like we can do IPv6. Making the socket works, but binding fails. It seems that this is a docker thing and that we'd need to configure the docker daemon? I found this stackoverflow post but it has no answers: https://stackoverflow.com/questions/75205327/configuring-docker-daemon-for-github-actions

Edit: also I removed musl-dev because https://github.com/python-trio/trio/pull/2939 should make that dependency not required.

[jakkdl]

Doesn't look like we can do IPv6. Making the socket works, but binding fails. It seems that this is a docker thing and that we'd need to configure the docker daemon? I found this stackoverflow post but it has no answers: https://stackoverflow.com/questions/75205327/configuring-docker-daemon-for-github-actions

Seems quite doable in theory then, but not worth the effort.