CI: fix deprecation warnings

[ThomasWaldmann]

Fixes the two deprecation warnings currently shown on CI runs.

lint: Node.js 20 deprecation

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: astral-sh/ruff-action@v3.

Bumped astral-sh/ruff-action v3 -> v4.1.0. Checked the manifests: v3.6.1 declares using: node20, v4.1.0 declares using: node24.

The exact version has to be pinned: with v4 astral-sh switched to immutable releases and no longer publishes a floating v4 major tag (only v4.0.0 and v4.1.0 exist), so @v4 does not resolve.

Ruff version resolution itself is unchanged (pyproject-discovered, else latest), and we don't pin ruff, so both v3 and v4 use the latest ruff.

vm_tests: deprecated run input

Input 'run' has been deprecated with message: The "run" parameter is deprecated. Use the custom shell (shell: cpa.sh {0}) on subsequent steps to run commands in the virtual machine instead.

Split the single cross-platform-actions/action step into a "Start VM" step plus a test step using the recommended custom shell:

- name: Start VM for ${{ matrix.display_name }}
  uses: cross-platform-actions/action@v1.3.0
  with:
    operating_system: ${{ matrix.os }}
    version: ${{ matrix.version }}
    shell: bash

- name: Test on ${{ matrix.display_name }}
  shell: cpa.sh {0}
  run: |
    ...

The test script itself is unchanged apart from a 2-space dedent — git diff -w shows only the two hunks above.

Two behaviour details that matter here:

• File sync: with shell: cpa.sh {0} the helper syncs runner->vm before the script and vm->runner after, so artifacts/*, test-results.xml and coverage.xml still reach the later upload steps.
• shutdown_vm: its default flips from true to false once run is gone, which is what we want here — the VM has to survive into the test step.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.70%. Comparing base (4a25abc) to head (6cf7dfd).
⚠️ Report is 3 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9960      +/-   ##
==========================================
+ Coverage   85.68%   85.70%   +0.01%     
==========================================
  Files          95       95              
  Lines       16799    16815      +16     
  Branches     2574     2577       +3     
==========================================
+ Hits        14394    14411      +17     
+ Misses       1669     1668       -1     
  Partials      736      736              

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