🧪 Add Ubuntu on ARM into the CI matrix

[webknjaz]

The respective dists are being built already. This patch moves building to faster native ARM runners and makes sure they are also tested.

Resolves #674.

[Copilot]

Pull Request Overview

This PR adds Ubuntu on ARM virtual machines to the CI testing matrix to ensure ARM distributions are properly tested alongside the existing x86_64 builds. The change expands test coverage by including ARM architecture testing in the GitHub Actions workflow.

• Adds ubuntu-24.04-arm to the CI matrix runner configurations
• Includes changelog documentation for the enhancement

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
.github/workflows/ci-cd.yml	Adds ubuntu-24.04-arm to the runner-vm-os matrix
docs/changelog-fragments/674.contrib.rst	Documents the CI enhancement with ARM Ubuntu VM testing
docs/changelog-fragments/761.contrib.rst	Contains incorrect filename reference for changelog fragment

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[webknjaz]

I accidentally pushed a43317f directly to devel. So I rebased this one on top.

[webknjaz]

The ssh_clientkey_path fixture is possibly being slow due to ssh-keygen -b 8192 hanging for noticable amount of time.

Thread 0x0000ff4b189205e0 (most recent call first):
  File "/opt/hostedtoolcache/Python/3.11.13/arm64/lib/python3.11/subprocess.py", line 2011 in _try_wait
  File "/opt/hostedtoolcache/Python/3.11.13/arm64/lib/python3.11/subprocess.py", line 2053 in _wait
  File "/opt/hostedtoolcache/Python/3.11.13/arm64/lib/python3.11/subprocess.py", line 1264 in wait
  File "/opt/hostedtoolcache/Python/3.11.13/arm64/lib/python3.11/subprocess.py", line 391 in call
  File "/opt/hostedtoolcache/Python/3.11.13/arm64/lib/python3.11/subprocess.py", line 408 in check_call
  File "/home/runner/work/pylibssh/pylibssh/tests/conftest.py", line 104 in ssh_clientkey_path
[...]

(https://github.com/ansible/pylibssh/actions/runs/17129398870/job/48589807624?pr=761#step:16:41)